JPH0515667B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an improvement in a method for manufacturing a silicon nitride sintered body. [Prior Art] Silicon nitride sintered bodies are attracting attention as structural ceramics. As a method for achieving high strength of this silicon nitride sintered body, efforts are being made to develop excellent sintering aids, improve silicon nitride raw material powder, and so on. [Problems to be Solved by the Invention] An object of the present invention is to provide a method for manufacturing a high-strength silicon nitride sintered body. [Means for Solving the Problem] As a result of research into a method for producing a high-strength silicon nitride sintered body, the inventors have determined the maximum and average particle diameters of silicon nitride powder, which is a raw material powder, and sintering aid powder. It was confirmed that by specifying the particle size ratio of silicon nitride powder and sintering aid powder within a certain range, it was possible to obtain a silicon nitride sintered body that was easy to prepare raw materials, had low raw material costs, and had high strength. However, the present invention has been completed. The method for manufacturing a silicon nitride sintered body of the present invention is a method for manufacturing a silicon nitride sintered body by molding and firing raw material powder that is a mixture of silicon nitride powder and sintering aid powder. The particle size is 5 microns or less and the average particle size is 1 micron or less, and the maximum particle size and average particle size of the sintering aid powder are 3/5 and 2/2 of the maximum particle size and average particle size of the silicon nitride powder, respectively. 3 or less and the average particle size of the sintering aid powder is larger than 0.05 micron. The manufacturing method of the present invention is characterized by the particle size of the silicon nitride powder as the raw material powder and the sintering aid powder.
The composition of the raw material powder other than the particle size of the raw material powder, the molding process, the sintering process, etc. are the same as those of the conventional method for producing a silicon nitride sintered body. In the manufacturing method of the present invention, the silicon nitride powder constituting the raw material powder has a maximum particle size of 5 microns or less and an average particle size of 1 micron or less. A preferable maximum particle size range is 0.5 to 5 microns, and a preferable average particle size range is 0.1 to 1 micron.
If the maximum particle size exceeds 5 microns and the average particle size exceeds 1 micron, a high-strength silicon nitride sintered body cannot be obtained. On the other hand, if the powder is made into a fine powder with a maximum particle size of 0.5 microns and an average particle size of less than 0.1 microns, the manufacturing cost of the powder will be high and its uses will be restricted.
In particular, silicon nitride, which is the main ingredient, is used in a large amount, so the increased cost becomes a big burden. The maximum particle size and average particle size of the sintering aid powder are 3/5 and 2/3 or less of the maximum particle size and average particle size of the silicon nitride powder, respectively, and the average particle size is larger than 0.05 micron. There needs to be. Also,
The maximum particle size of the sintering aid powder is preferably 0.2 to 2 microns, and the average particle size is preferably greater than 0.05 microns and less than 0.5 microns. When the maximum particle size and average particle size of the sintering aid powder exceed 3/5 and 2/3 of the maximum particle size and average particle size of the silicon nitride powder, respectively, a high-strength silicon nitride sintered body is produced. is not obtained. On the other hand, if the sintering aid powder is made into ultrafine particles with an average particle size of 0.05 microns or less, the manufacturing cost of the powder becomes extremely high, which is not preferable. As the sintering aid, itria, alumina, magnesia, and spinel, which is a double oxide of a divalent metal oxide and an oxidized metal oxide, are used as in the past. The blending ratio of the sintering aid is about 4 to 10 parts by weight based on 100 parts by weight of silicon nitride powder, similar to the conventional method for producing a silicon nitride sintered body. In addition, also in the manufacturing method of the present invention, the silicon nitride powder and the sintering aid powder need to be mixed as uniformly as possible. For this purpose, it is necessary to thoroughly mix the silicon nitride powder and the sintering aid powder using a pole mill or other known appropriate method. In the process of manufacturing a ceramic molded body from this raw material powder, the conventional manufacturing process of ceramic molded bodies can be used as is. For example, a ceramic injection molding method can be used to produce a ceramic molded body with a complicated shape. Ceramics injection molding method mixes resin with raw material powder,
After a certain amount of kneaded material is formed, it is injection molded using the same method as ordinary injection molding of plastics, and the molded product is heated to remove the resin to form a ceramic molded product (green compact). It is also possible to produce a compacted ceramic molded body by putting raw material powder into a mold and compressing it with a press or the like. Furthermore, a ceramic molded body can be manufactured by a method such as slip casting. As for the sintering process, the sintering process of the conventional method for producing ceramic sintered bodies can be adopted as is. That is, the above ceramic molded body is heated at 1650 to 1800° C. for 1 to 4 hours in a nitrogen gas atmosphere to form a silicon nitride sintered body. [Operations and Effects of the Invention] In the manufacturing method of the present invention, the particle sizes of the silicon nitride powder and the sintering aid powder, which are the raw material powders, are in the submicron range, so they can be prepared relatively easily.
And raw material costs are low. Moreover, since the particle size is within a range that is easy to sinter, sintering becomes easy and a silicon nitride sintered body with excellent high strength can be obtained. The silicon nitride sintered body manufactured by the manufacturing method of the present invention is a high-strength silicon nitride sintered body that has a strength of about 20 kg/mm _N at room temperature compared to the silicon nitride sintered body obtained by the conventional manufacturing method. becomes. [Example] The following is a description using test examples. Test example 1 Maximum particle size as silicon nitride powder: 10 μm, average particle size
2 μm silicon nitride powder was obtained. This commercially available silicon nitride powder was ground in a ball mill, with a maximum particle size of 5μ,
Silicon nitride powder with an average particle size of 1μm, maximum particle size of 2.5μm,
Silicon nitride powder with average particle size of 0.5μm, maximum particle size of 0.5μm
Four types of silicon nitride powders with different particle sizes were prepared using silicon nitride powder with a maximum particle size of 10 μm and an average particle size of 2 μm as commercially available. Next, ittria 5 was used as a sintering aid.
A sintering aid powder consisting of a mixed raw material of 3 parts by weight of alumina and 3 parts by weight was prepared. This sintering aid powder was also pulverized in a ball mill by changing the degree of pulverization to obtain the maximum particle size.
5μm, average particle size 1μm sintering aid powder, maximum particle size
2μm, average particle size 0.5μm sintering aid powder, maximum particle size
A total of four types of sintering agent powder were obtained, including a sintering aid powder with a maximum particle size of 0.2 μm and an average particle size of 0.05 μm. Next, seven raw material powders shown in Table 1 were prepared by combining the above four types of silicon nitride powders and the above four types of sintering aid powders. In addition, each raw material powder had a composition ratio of 92% by weight of silicon nitride powder and 8% by weight of sintering aid powder. Next, mix the above raw material powders in a ball mill,
After drying, it was finally hydrostatically pressed at 1.2 ton/cm _N to obtain a ceramic compact, which was then sintered at 1800° C. for 2 hours in nitrogen gas at 10 atm to produce a silicon nitride sintered compact. In addition, for one type of raw material powder, 5 mm
Twenty rod-shaped test pieces each measuring 3 mm x 35 mm were manufactured. These test pieces were subjected to a three-point bending test at room temperature to measure their bending strength Kgf/ _mmN . The results obtained are shown in Table 1. From Table 1, the maximum particle size of the silicon nitride powder is 5 μm or less, the average particle size is 1 μm or less, and the maximum particle size of the sintering aid is 2 μm or less, the average particle size is 0.5 μm or less, and The maximum particle size of the auxiliary agent is 3/5 or less of the maximum particle size of the silicon nitride powder, and the sintering aid powder is flat.

[Table] △: The particle size of the sintering aid is outside the range of the particle size of the sintering aid of the present invention ×: Low strength

[Table] △: The particle size of the sintering aid is outside the range of the particle size of the sintering aid of the present invention ×: Raw material powder with low strength and an average particle size of 2/3 or less of the average particle size of the silicon nitride powder The bending strengths of No. 2, No. 4, No. 5, and No. 7, which were used, were 85 to 105. On the other hand, No. 1, No. 3, and No. 3, in which the particle size ratio of silicon nitride powder and sintering aid powder do not fall within the particle size ratio of the present invention.
The silicon nitride sintered body obtained using the raw material powder No. 6 had a sintering strength of 65 to 74, which revealed that the strength was low. Test Example 2 Ittria 5 was used instead of the sintering aid powder in Test Example 1.
A mixed powder of 5 parts by weight of magnesia alumina spinel was used as a sintering aid. Test Example 1 also applies to this ittria and spinel-based sintering aid.
Grind with a ball mill in the same way as before, with a maximum particle size of 2 μm,
Sintering aid powder with average particle size of 0.5μm, maximum particle size of 0.4μm
Three types of sintering aid powders were prepared: m, average particle size of 0.1 μm, maximum particle size of 0.2 μm, and average particle size of 0.05 μm. As for silicon nitride powder, which is the main raw material, the same four types of silicon nitride powder as in Test Example 1 were used. These silicon nitride powders and sintered material powders are
Seven types of raw material powders were prepared by blending in the combinations shown in the table. Each raw material powder was shaped and fired in the same manner as in Test Example 1, and 20 test pieces were created for each. Thereafter, a three-point bending test was conducted in the same manner to measure the bending strength. The results are also shown in Table 2. From Table 2, it is clear that when the particle size ratio of the silicon nitride powder and the sintering aid powder falls within the particle size ratio of the present invention, the strength of the sintered body is improved by about 20 Kgf/ _mmN .

Claims (1)

[Scope of Claims] 1. A method for manufacturing a silicon nitride sintered body by molding and firing a raw material powder obtained by mixing silicon nitride powder and sintering aid powder, wherein the maximum particle size of the silicon nitride powder is 5 microns or less. , the average particle size is 1 micron or less, the maximum particle size and average particle size of the sintering aid powder are 3/5 and 2/3 of the maximum particle size and average particle size of the silicon nitride powder, respectively, and the sintering A method for producing a silicon nitride sintered body, characterized in that the average particle size of the auxiliary powder is larger than 0.05 microns. 2. The manufacturing method according to claim 1, wherein the sintering aid is one or more of itria, magnesia, alumina, and spinel.