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

Abstract

Provided is a method whereby a ceramic powder can be more evenly mixed with a sintering aid. This method for producing a mixed ceramic powder includes: a step in which a sintering aid comprising granules of a sintering-aid powder is prepared; and a step in which a ceramic powder serving as a base material is mixed with at least one such sintering aid to produce a mixed ceramic powder.

Description

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

[0001] The embodiments relate to a method for producing a ceramic mixed powder and a method for producing a ceramic sintered body.

[0002] There are various ceramic sintered bodies made of silicon nitride, aluminum nitride, aluminum oxide, zirconium oxide, etc. They are used in a wide range of fields, including substrates for semiconductor devices, bearing balls, rollers, heat-resistant containers, and engine parts.

[0003] It is known that a silicon nitride substrate made of sintered silicon nitride is able to achieve both thermal conductivity and strength, and that a bearing ball made of sintered silicon nitride is able to achieve both wear resistance and processability.

[0004] The manufacturing process of a ceramic sintered body includes a mixing step of mixing raw material powders, a molding step, a degreasing step, and a sintering step. The manufacturing process of a ceramic sintered body includes adding a sintering aid to the ceramic powder that serves as the base material. The use of a sintering aid can improve sinterability. The use of a sintering aid is also effective in improving the properties of the ceramic sintered body.

[0005] On the other hand, the use of a sintering aid requires that the ceramic powder serving as the base material and the sintering aid be mixed uniformly. To achieve this uniform mixing, a crushing and mixing process is carried out using a ball mill or the like.

[0006] Patent No. 7319607 Patent No. 6416088 Japanese Patent Application Publication No. 6-172011 Publication No. 7-116533

[0007] A ball mill can break down agglomerated powder and stabilize the particle size distribution. It is known that powder processed in a ball mill is, for example, granulated to form granulated powder. Granulated powder has excellent fluidity. Granulated powder with excellent fluidity improves the filling ability into a mold.

[0008] For example, it is known to use a ball mill with a grinding material called media. Adding media improves the crushability of ceramic powder. However, in ball mills, small powder particles tend to adhere to the inner wall of the rotating vessel or the media. The media cannot fully remove the powder that adheres to the inner wall. When powder adheres to the inner wall or media, problems arise such as an error in the mixing ratio with the sintering aid. This error in the mixing ratio causes a decrease in the yield of sintered ceramics.

[0009] The embodiments address these issues and provide a method that can improve the uniformity of mixing of ceramic powder and sintering aid.

[0010] A method for producing a ceramic mixed powder according to an embodiment includes a step of preparing a sintering aid containing a granulated powder of a sintering aid powder, and a step of mixing a ceramic powder as a base material with at least one sintering aid to produce a ceramic mixed powder.

[0011] 1 is a diagram showing an example of a process flow for a ceramic sintered body according to an embodiment; FIG. 2 is a diagram showing another example of a process flow for a ceramic sintered body according to an embodiment; FIG. 3 is a diagram showing an example of a ceramic sintered body according to an embodiment;

[0012] The method for producing a ceramic mixed powder according to the embodiment includes the steps of preparing a sintering aid containing a granulated powder of a sintering aid powder, and mixing a ceramic powder serving as a base material with at least one sintering aid to produce a ceramic mixed powder.

[0013] 1 and 2 show an example of a process flow for a ceramic sintered body according to an embodiment. Fig. 1 shows an example in which a granulated powder of a sintering aid is used. Fig. 2 shows an example in which both a granulated powder of a sintering aid and an ungranulated sintering aid are used.

[0014] First, ceramic powder to be used as the base material is prepared. The base material is the component that is contained in the largest amount among the total of the ceramic powder and the sintering aid powder. When the total of the ceramic powder to be used as the base material and the sintering aid powder is taken as 100 mass %, the ceramic powder to be used as the base material is preferably 70 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass %. As the ceramic powder to be used as the base material, silicon nitride (sialon (Si ３ N ４ ・Al ２ O ３ )), aluminum nitride, aluminum oxide, zirconium oxide, and the like powders.

[0015] A sintering aid is also prepared. Examples of the sintering aid include powders or granulated powders of one or more (at least one) compounds selected from 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 compounds selected from yttrium and lanthanoid elements. Examples of compounds include oxides, nitrides, silicides, carbides, and composite compounds thereof. Furthermore, when the total amount of the ceramic powder serving as the base material and the sintering aid powder is taken as 100% by mass, the amount of the sintering aid is preferably 1% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 15% by mass or less.

[0016] The process of preparing granulated powder of sintering aid powder is a process of preparing at least a portion of the sintering aid powder to be used as granulated powder. Granulation is the process of forming a "granular material." Granulated powder is a powder with a larger average particle size than the sintering aid powder used for granulation. Granulated powder may be formed by mixing a sintering aid and a binder and solidifying the mixture into granules. When only one type of sintering aid is used, that granulated powder is used. Powder of sintering aid A and granulated powder of sintering aid A may also be used.

[0017] When multiple types of sintering aids are used, some or all of the granulated powders are used. An example will be described in which three types of sintering aids, sintering aid A, sintering aid B, and sintering aid C, are used as sintering aids. The process of preparing at least a portion of the sintering aid powder to be used as granulated powder involves using one or more of granulated powder of sintering aid A, granulated powder of sintering aid B, and granulated powder of sintering aid C. Granulated powder formed by mixing two or more of granulated powder of sintering aid A, granulated powder of sintering aid B, and granulated powder of sintering aid C may also be used. While FIG. 2 illustrates an example in which three types of sintering aids are used, two or more types of sintering aids may be used. Therefore, using multiple types of sintering aids means using multiple sintering aids with different components.

[0018] In this way, in the mixing step of mixing the ceramic powder as the base material with the sintering aid, it is effective to mix granulated powder of the sintering aid. It is preferable that all of the sintering aid to be added is granulated powder, but it is not necessary that all of it is granulated powder.

[0019] The granulated powder is preferably formed using a single type of sintering aid. Forming the granulated powder using the same sintering aid makes it easier to control the amount of sintering aid added. Granulated powder of the ceramic powder used as the base material may be used, but is preferably not used. Similarly, granulated powder consisting of a mixture of the ceramic powder used as the base material and the sintering aid powder may be used, but is preferably not used. As mentioned above, rare earth compounds are used as sintering aids. Sintering aids are often heavier components than the ceramic powder used as the base material. For granulated powders of the same size, containing heavier components improves fluidity. This increases the scraping effect. In other words, the granulated powder of the sintering aid preferably contains heavier components than the ceramic powder used as the base material. Examples of heavy components include rare earth compounds. Examples of rare earth elements include Y (yttrium) and lanthanoid elements. Therefore, the granulated powder of the sintering aid preferably contains a rare earth compound in an amount of 2% by mass to 10% by mass. When a plurality of types of sintering aids are used, it is preferable that the sintering aid contains the rare earth compound in the largest amount.

[0020] Next, the ceramic powder as the base material and the granulated powder of the sintering aid are mixed together. If necessary, a binder, a solvent, etc. may be added to form a slurry before the mixing step.

[0021] The mixing step is preferably carried out using a crusher such as a ball mill or a bead mill. An example of a ball mill is a crusher using media with a diameter of about 4 to 30 mm. An example of a bead mill is a crusher using media with a diameter of 3 mm or less. Using media can improve crushing efficiency.

[0022] For example, when using a ball mill, the mixing process is performed by rotating a grinding chamber called a vessel. When using a bead mill, the mixing process is performed by rotating a propeller-shaped stirrer called a disk. Both mixing processes involve rotation, and ceramic powder and sintering aid powder tend to adhere to the inner walls of the grinder. As described below, ceramic powder and sintering aid powder are fine powders with an average particle size of 5 μm or less. The centrifugal force associated with rotation makes them prone to adhering to the inner walls of the grinder. Static electricity generates, causing the fine powders to agglomerate, making them more likely to adhere to the inner walls of the grinder. This is because the raw powder material itself is an insulator and therefore prone to static electricity.

[0023] This has the effect of scraping off the ceramic powder and sintering aid powder adhering to the inner walls of the pulverizer with the granulated powder of the sintering aid powder. If the ceramic powder and sintering aid powder remain adhering to the inner walls of the pulverizer, it may cause deviation in the mixing ratio.

[0024] The media are formed of hard materials such as ceramic sinters, tungsten carbide (WC), and stainless steel. Examples of ceramic sinters used for the media include silicon carbide sinters, aluminum oxide sinters, zirconium oxide sinters, and silicon nitride sinters. The media wears the inner walls of the mill, and the media also wears against each other, causing contamination. If conditions are set to suppress media wear in order to prevent contamination, the processing time will be extended and productivity will decrease.

[0025] The ceramic powder of the embodiment is produced using sintering aid granulated powder. By using the sintering aid granulated powder, the amount of media mixed can be reduced. Because the sintering aid granulated powder is not a hard material like the media, it does not wear down the inner wall. Even if the sintering aid granulated powder particles collide with each other and are destroyed, it does not cause a deviation in the mixing ratio.

[0026] 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. The minimum value of the average particle size of the sintering aid granulated powder is not particularly limited, but 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. For this reason, the average particle size of the sintering aid granulated powder is preferably in the range of 0.5 mm to 10 mm, and more preferably 1 mm to 5 mm.

[0027] The average particle size of the sintering aid granulated powder is measured using a photograph containing 100 randomly selected sintering aid particles. The photograph can be taken using a device such as a metallurgical microscope or a scanning electron microscope (SEM). The longest diagonal line of each granulated powder in the photograph is taken as the particle size, and the average value of these is taken as the average particle size.

[0028] The average particle size of the sintering aid powder is preferably 3 μm or less. If the average particle size is larger than 3 μm, it may be difficult to adjust the size of the granulated powder. There is no particular limit to the lower limit of the average particle size of the sintering aid powder, but it is preferably 0.1 μm or more. If the average particle size is less than 0.1 μm, aggregation is likely to occur. Particles are also likely to adhere to the inner wall of the grinder due to static electricity. For this reason, the average particle size of the sintering aid powder is preferably in the range of 0.1 μm or more and 3 μm or less, and more preferably 0.5 μm or more and 2 μm or less. The average particle size of the sintering aid powder is D ５０ The average particle size of the sintering additive powder is defined by the average particle size measured by, for example, a laser diffraction particle size distribution measuring device.

[0029] The ceramic powder used as the base material preferably has an average particle size of 5 μm or less, and a maximum particle size of 20 μm or less.

[0030] If the average particle size of the ceramic powder used as the base material exceeds 5 μm, uniform dispersion with the sintering aid may be hindered. The lower limit of the average particle size of the ceramic powder used as the base material is not particularly limited, but 0.1 μm or more is preferable. If the average particle size is less than 0.1 μm, aggregation is likely to occur. Particles are also likely to adhere to the inner wall of the grinder due to static electricity. For this reason, the average particle size of the ceramic powder used as the base material is preferably in the range of 0.1 μm to 5 μm, and more preferably 0.5 μm to 3 μm. The average particle size of the sintering aid powder is D ５０ , that is, the median diameter is used.

[0031] If the maximum particle size of the ceramic powder used as the base material exceeds 20 μm, it will cause coarse grains in the sintered body. Coarse grains may cause defects in the ceramic sintered body or a decrease in strength. For this reason, it is preferable that the maximum particle size of the ceramic powder used as the base material is 20 μm or less, and more preferably 10 μm or less. The maximum particle size of the ceramic powder used as the base material is D １００ The average particle size D ５０ and maximum particle size D １００ The measurement sample is 1 g.

[0032] The ceramic powder used as the base material is preferably one or more powders selected from silicon nitride (including sialon), aluminum nitride, aluminum oxide, and zirconium oxide. Ceramic powders using silicon nitride as the base material produce silicon nitride sintered bodies. Ceramic powders using aluminum nitride as the base material produce aluminum nitride sintered bodies. Ceramic powders using aluminum oxide as the base material produce aluminum oxide sintered bodies. Ceramic powders using zirconium oxide as the base material produce zirconium oxide sintered bodies. Silicon (Si) may also be used as the base material. Silicon nitride sintered bodies can be obtained from silicon-based ceramic powders by reactive sintering using a nitriding reaction. The sinterability of these ceramic sintered bodies can be improved by adding a sintering aid. In other words, the addition of a sintering aid is essential. The use of sintering aid granulated powder can suppress variations in the mixing ratio of the base material and sintering aid. This suppresses variations in the performance of the ceramic sintered bodies.

[0033] The sintering aid granulated powder may not contain an organic binder. The mixing process of the ceramic powder serving as the base material and the sintering aid granulated powder includes mixing the base material and the sintering aid. If the sintering aid granulated powder does not contain an organic binder, the granulated powder is easily broken down during the mixing process. This makes it possible to shorten the time required to achieve uniform dispersion while achieving the effect of scraping off deposits on the inner wall of the grinder. In other words, when using sintering aid granulated powder containing an organic binder, uniform dispersion can be achieved by extending the mixing time.

[0034] The mixing step is preferably carried out using a crusher such as a ball mill or a bead mill. For example, in the case of a ball mill, the rotation speed of the rotating container is preferably in the range of 10 rpm to 300 rpm, more preferably 10 rpm to 250 rpm.

[0035] By performing a process of preparing a mixed powder by mixing the ceramic powder serving as the base material according to the embodiment with the granulated sintering additive, it is possible to suppress deviation in the mixing ratio. By this process, a ceramic mixed powder can be obtained.

[0036] Next, a process for producing a compact is performed using the mixed powder obtained by the method for producing a ceramic mixed powder according to the embodiment. Various methods can be used for compacting, such as doctor blade molding, mold compacting, injection molding, casting, rolling granulation, and cold isostatic pressing (CIP). A compact can be obtained through this process. Furthermore, when performing the compacting process, an organic binder or the like may be added to the mixed powder. The organic binder is preferably in the range of 5 to 30 parts by mass per 100 parts by mass of the mixed powder. Furthermore, when performing the compacting process, a solvent may be added when preparing a slurry containing the mixed powder. Examples of the solvent include aqueous solvents and organic solvents. For example, when using the doctor blade method, the slurry viscosity is preferably in the range of 5,000 to 15,000 cps. The compact may be subjected to a degreasing process, if necessary. In the embodiment, unless otherwise specified, the degreased body is included in the compact.

[0037] Next, the compact is sintered. Various methods can be used for the sintering process, such as atmospheric sintering, gas pressure sintering, hot pressing, hot isostatic pressing (HIP), and reaction sintering. The sintering temperature can be 1500°C or higher and 2000°C or lower. Various sintering atmospheres can be used, such as air, inert gas, and vacuum.

[0038] A ceramic sintered body can be obtained by the above steps. If necessary, a honing step, a cleaning step, a polishing step, etc. are performed. FIG. 3 is a diagram showing an example of a ceramic sintered body. FIG. 3 shows a substrate 1 made of a ceramic sintered body. FIG. 3 shows an example in which the substrate 1 is rectangular parallelepiped-shaped, but the substrate 1 is not limited to this, and may have other shapes such as a square, a circle, a triangle, etc.

[0039] The method for manufacturing a ceramic sintered body according to the embodiment can suppress variations in the mixing ratio of ceramic raw material powders. This reduces variations in the properties of the resulting ceramic sintered body. In particular, it is possible to reduce variations between lots, improving mass productivity. Examples of properties for which variations can be suppressed include strength and insulation properties.

[0040] (Examples 1 to 6, Comparative Examples 1 and 2) Silicon nitride powder or aluminum nitride powder was prepared as the ceramic powder that serves as the base material, and sintering aid powder was prepared. At least a portion of the sintering aid is granulated powder. The combinations are shown in Tables 1 and 2. The mixing ratio is based on the total of the ceramic powder that serves as the base material and the sintering aid powder being 100 mass %. Table 2 shows the particle size of the granulated powder for the sintering aid powder that is granulated powder.

[0041]

[0042]

[0043] Next, the ceramic powder serving as the base material and the sintering additive powder were mixed using a ball mill. The conditions for the ball mill are shown in Table 3.

[0044]

[0045] The amount of powder fed into the ball mill was the same for Examples 1 to 6 and Comparative Examples 1 and 2. After ball milling, the amount of adhesion on the inner wall of the ball mill was confirmed. The amount of adhesion was confirmed visually after stopping the device one hour after starting the ball milling. The amount of adhesion in Examples 1 to 4 was determined based on Comparative Example 1. If the amount was equal to or greater than the amount in Comparative Example 1, it was judged as "high." If the amount was less than the amount in Comparative Example 1, it was judged as "low." Furthermore, the amount of adhesion in Examples 5 and 6 was determined based on Comparative Example 2. If the amount was equal to or greater than the amount in Comparative Example 2, it was judged as "high." If the amount was less than the amount in Comparative Example 2, it was judged as "low." When the amount of adhesion was confirmed, it was judged to be low in Examples 1 to 6. On the other hand, a large amount of adhesion was observed in the Comparative Example. A low amount of adhesion in the initial stage of ball milling indicates high uniformity in the mixing of the ceramic powder serving as the base material and the sintering aid powder in the initial stage.

[0046] After the mixing process, a binder, a solvent, and the like were added to prepare a slurry. The slurry was prepared by adding 10 parts by mass of an organic binder to 100 parts by mass of the mixed powder, so that the viscosity was approximately 7000 cps. The slurry was then formed into a sheet using a doctor blade method. The resulting sheet (green sheet) was cut to a predetermined size and subjected to a sintering process. This process yielded a ceramic sintered substrate measuring 100 mm long, 80 mm wide, and 0.32 mm thick. Five batches of each were performed.

[0047] The three-point bending strength and dielectric strength of each ceramic sintered substrate were measured. The average values ​​between lots and the minimum and maximum values ​​were investigated. The three-point bending strength was measured in accordance with JIS-R-1601 (2008). The dielectric breakdown voltage was measured in accordance with the dielectric breakdown strength test of JIS-C-2141 (1992). The results are shown in Table 4.

[0048]

[0049] As can be seen from Table 4, there was no significant difference in the average values ​​of three-point bending strength and dielectric strength voltage between Examples 1 to 6 and Comparative Examples 1 and 2. On the other hand, the range between the minimum and maximum values ​​for Examples 1 to 6 was narrow compared to the average values. This shows that the characteristic variations were suppressed in Examples 1 to 6. Therefore, it was found that using sintering aid granulated powder is effective in suppressing the variations in characteristics such as strength and dielectric strength voltage.

[0050] 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. The above-described embodiments can be implemented in combination with each other.

Claims

1. A method for producing a ceramic mixed powder, comprising: a step of preparing a sintering aid containing a granulated powder of a sintering aid powder; and a step of mixing a ceramic powder as a base material with the at least one sintering aid to produce a ceramic mixed powder.

2. The method for producing a ceramic mixed powder according to claim 1, wherein the granulated powder of the sintering additive powder includes granulated powders of a plurality of sintering additive powders.

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

4. The method for producing a ceramic mixed powder according to claim 1 or 2, wherein the granulated powder of the sintering additive powder has an average particle size of 10 mm or less.

5. The method for producing a ceramic mixed powder according to claim 3, wherein the granulated powder of the sintering additive powder has an average particle size of 10 mm or less.

6. The method for producing a ceramic mixed powder according to claim 1 or 2, wherein the sintering aid powder has an average particle size of 3 μm or less.

7. The method for producing a ceramic mixed powder according to claim 5, wherein the sintering aid powder has an average particle size of 3 μm or less.

8. The method for producing a ceramic mixture powder according to claim 1 or 2, wherein the ceramic powder comprises at least one ceramic powder selected from the group consisting of silicon nitride powder, aluminum nitride powder, aluminum oxide powder, and zirconium oxide powder.

9. The method for producing a ceramic mixture powder according to claim 6, wherein the ceramic powder comprises at least one ceramic powder selected from the group consisting of silicon nitride powder, aluminum nitride powder, aluminum oxide powder, and zirconium oxide powder.

10. A method for producing a ceramic mixed powder according to claim 1 or 2, wherein the ceramic powder has an average particle size of 5 μm or less, and a maximum particle size of 20 μm or less.

11. The method for producing a ceramic mixed powder according to claim 8, wherein the ceramic powder has an average particle size of 5 μm or less, and a maximum particle size of 20 μm or less.

12. The method for producing a ceramic mixed powder according to claim 1 or 2, wherein the granulated powder of the sintering additive powder does not contain an organic binder.

13. The method for producing a ceramic mixed powder according to claim 6, wherein the granulated powder of the sintering additive powder does not contain an organic binder.

14. A method for producing a ceramic sintered body, comprising the steps of: preparing a compact using the mixed powder obtained by the method for producing a ceramic mixed powder according to claim 1; and sintering the compact.

15. A method for producing a ceramic sintered body, comprising the steps of: preparing a compact using the mixed powder obtained by the method for producing a ceramic mixed powder according to claim 7; and sintering the compact.

16. A method for producing a ceramic sintered body, comprising: a step of producing a compact using a mixed powder obtained by the method for producing a ceramic mixed powder according to claim 10; and a step of sintering the compact.

17. A method for producing a ceramic sintered body, comprising the steps of: preparing a compact using a mixed powder obtained by the method for producing a ceramic mixed powder according to claim 11; and sintering the compact.

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