JP2005298299A - Silicon nitride-based disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride-based disk without corrosion caused by molten copper in the case of producing a copper powder by a centrifugal atomization method. <P>SOLUTION: A blended matter containing by silicon nitride of 60-80 mass%, aluminum nitride of 15-24 mass%, alumina of 2-8 mass% and yttria of 2-8 mass% is sintered and its crystal phase contains Y<SB>0.54</SB>(Si<SB>9.57</SB>Al<SB>2.43</SB>)(O<SB>0.81</SB>N<SB>15.19</SB>) and β-Si<SB>3</SB>N<SB>4</SB>or β-sialon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a disk used in a metal powder manufacturing apparatus by centrifugal spraying, and more particularly to a silicon nitride disk used for manufacturing copper powder.

  Metal powder is used in various fields such as powder metallurgy. For example, copper powder has wide usage such as PTA welding material, brazing material, conductive paste, MIM, magnetic shield material (for surface treatment). . Among them, submicron-class true sphere copper powder has the following characteristics: (1) good fluidity (2) high packing density (3) low specific surface area resulting in low viscosity during pasting There is a growing need.

  As a method for producing the metal powder, a water atomizing method, a gas atomizing method, a centrifugal spraying method, an electrolysis method and the like are generally used. Among these, the centrifugal spraying method has an advantage that the particle diameter of 100 μm or less can be easily controlled and becomes a true sphere. In this method, when molten metal is dropped onto a disk rotating at high speed, a molten metal is sprayed horizontally from the outer periphery of the disk, and then solidified to produce a spherical metal powder.

  As an example of producing copper powder by the centrifugal spray method, there is Patent Document 1, in which a large disk of φ80 × 40 made of metal (material SC37) is used. In this case, the rotational speed of the disk is as low as 5000 rpm, and the weight of the disk is large, so that high-speed rotation cannot be performed and it is impossible to produce fine powder.

  In general, when the melting temperature of the metal is low, the material of the disk may be metal, but when the melting temperature of the metal is high, ceramics are used. Ceramics with a small specific gravity are also suitable for increasing the rotational speed.

For example, Patent Document 2 describes a method for producing a thermoelectric material by centrifugal spraying. As a disk material, a silicon nitride material is used in which 90% β sialon containing 94.8% Si ₃ N ₄ is mixed with about 10% Y ₂ O ₃ or SiO ₂ glass. It is described that a powder thermoelectric material having an average particle size smaller than the conventional one can be manufactured with a high yield by using a rotating disk made of a material containing silicon nitride. However, the disk having this composition has a problem in durability when the molten temperature exceeds 1000 ° C.

Furthermore, when the present inventor used sialon as a disk for centrifugal spraying of molten copper, corrosion progressed from the center of the disk and the surface of the disk became unsmooth, so that the spray was not stable and the spray was not stable for a long time (1 hour It was found that there was a problem that the continuous operation of the above was not possible and the productivity was very low. It is estimated that this is because about 10% of the glass phase containing Al ₂ O ₃ and Y ₂ O ₃ in the sialon structure is melted by chemical reaction due to wear by molten copper or oxidation of molten copper. .
JP 58-91101 A JP 2002-151752 A

  Accordingly, the problem to be solved by the present invention is to provide a silicon nitride disk that is free from corrosion by molten copper in the production of copper powder by centrifugal spraying.

In order to solve the above problems, the present inventors crystallized the glass component by adding Al content in order to reduce as much as possible the glass component caused by alumina and yttria produced during sintering of sialon or silicon nitride. Focused on making it. As a result, it was found that by adding Al, the glass phase disappears, a plurality of crystal phases are generated, and the erosion resistance to the molten copper is dramatically improved. This crystal phase is Y _0.54 (Si _9.57 Al _2.43 ) (O _0.81 N _15.19 ), βSi ₃ N ₄ , Si ₃ Al ₇ O ₃ N ₉ , Y ₂ Si ₃ N ₄ O It was confirmed by X-ray analysis that it was ₃ mag.

Here, the Al component, when added with alumina (Al 2 _{O 3),} oxygen becomes excessive, the glass phase is increased, melting loss resistance to the molten copper is reduced to the contrary. On the other hand, when aluminum nitride (AlN) is added, Al or O is immobilized in the crystal as a compound having a sialon (Si—Al—O—N) composition or an α-type sialon, and a glass phase is not easily generated. . Therefore, the reaction between the reactive active copper and O in the molten state is suppressed. Therefore, it is important to use aluminum nitride as the Al content.

  Moreover, thermal conductivity becomes high because a glass phase turns into a crystal phase. For this reason, the temperature distribution difference between the surface and the inside at the time of heating the disk is eliminated, and the generated thermal stress can be reduced, so that it is possible to avoid cracking due to thermal shock during heating or when molten copper is dropped.

  The present invention has been made on the basis of the above knowledge, and the silicon nitride disk of the present invention has 60-80 mass% silicon nitride, 15-24 mass% aluminum nitride, 2-8 mass% alumina, and 2-8 yttria. A compound containing mass% is sintered.

The crystal phase in the silicon nitride disk of the present invention is such that the crystal phase is Y _0.54 (Si _9.57 Al _2.43 ) (O _0.81 N _15.19 ) and βSi ₃ N ₄ or β sialon. Including.

  In the silicon nitride disk of the present invention, the strength is reduced by the appearance of the second crystal phase in the single crystal phase of sialon or silicon nitride, but within the scope of the present invention, The bending strength is 300 MPa or more, and the strength sufficient to withstand the centrifugal force of high-speed rotation as a disk can be secured.

  By using the silicon nitride-based disk of the present invention as a disk for producing copper powder by centrifugal spraying, corrosion by molten copper is eliminated when molten copper is dropped and sprayed, enabling long-time operation. Thus, it was possible to stably and efficiently produce a true spherical copper powder having a particle size of 100 μm or less.

  The silicon nitride disk of the present invention is obtained by sintering a composition containing silicon nitride, aluminum nitride, alumina, and yttria.

  Silicon nitride can be used without any problem as long as it is commercially available as a ceramic raw material, and the blending amount is in the range of 60 to 80% by mass. When the blending amount is less than 60% by mass, characteristics such as high strength and thermal shock resistance characteristic of silicon nitride are impaired. When the blending amount exceeds 80% by mass, the amount of aluminum nitride added as an Al component and the glass liquid during sintering are reduced. While the phases are formed at the crystal grain boundaries, the amount of alumina and yttria, which function as an auxiliary agent for sintering silicon nitride, is relatively insufficient, and a high-strength silicon nitride-based disk with excellent corrosion resistance cannot be obtained.

  As aluminum nitride, any material that is generally commercially available as a ceramic raw material can be used without any problem, and the blending amount is in the range of 15 to 24% by mass. If the blending amount is less than 15% by mass, the crystallization of the glass phase present at the grain boundaries of silicon nitride, which is the object of the present invention, is not sufficient, and if it exceeds 24% by mass, the strength of the sintered body decreases, Since the characteristics of the original silicon nitride are impaired, it is not suitable as a disk for a centrifugal sprayer.

  Alumina can be used without any problem as long as it is commercially available as a ceramic raw material, and its blending amount is in the range of 2 to 8% by mass. When the blending amount is less than 2% by mass, the amount of alumina functioning as an auxiliary agent for sintering silicon nitride is insufficient, and a high-strength silicon nitride disk excellent in corrosion resistance cannot be obtained. On the other hand, when the blending amount exceeds 8% by mass, the glass component increases, and the silicon nitride disk having excellent corrosion resistance cannot be obtained.

  As yttria, any commercially available ceramic raw material can be used without any problem, and its blending amount is in the range of 2 to 8% by mass. If the blending amount is less than 2% by mass, the amount of yttria that functions as an auxiliary agent for sintering silicon nitride is insufficient, and a high-strength silicon nitride-based disk excellent in corrosion resistance cannot be obtained. On the other hand, when the blending amount exceeds 8% by mass, the glass component increases, and a silicon nitride disk having excellent corrosion resistance cannot be obtained.

  The silicon nitride disk of the present invention can be manufactured by a general silicon nitride or sialon manufacturing method. For example, it can be produced by the following production method.

First, water, a molding aid, and the like are added to a blend of a predetermined amount of silicon nitride, aluminum nitride, alumina, and yttria. The resulting slurry is granulated with a spray dryer or the like to obtain a compound for press molding. Next, the obtained compound is filled into a cylindrical rubber having a predetermined size, sealed, and then subjected to CIP treatment at a molding pressure of 1 ton / cm ² or more. Here, in place of the CIP process, there is no problem even if molding is performed by uniaxial pressing using a mold having a predetermined size. The obtained molded body is green processed to a predetermined size, degreased, and fired in a nitrogen atmosphere at 1650 to 1800 ° C. to obtain a sintered body of silicon nitride or sialon. The sintered body is ground to a predetermined dimensional accuracy, and then used as a disk for centrifugal spraying.

  If the casting method is applied instead of the above-mentioned manufacturing method, the above slurry is cast into a plaster mold or a resin mold, and the disk shape is directly molded, the manufacturing process is simplified and without green processing. Degreasing and firing are possible. In addition to the casting method, an injection molding method is also applicable.

  Various raw materials, water, and molding aids were added at the blending ratios shown in Table 1, mixed with a ball mill, and granules were produced with a spray dryer. Each granule was filled in a φ90 × 90 rubber mold and then CIP molded. The molded body was green processed into an umbrella-shaped disk shape of φ45 × L40. After degreasing and firing, grinding was performed to a predetermined dimensional accuracy to obtain a disk shape shown in FIG.

Further, a part of the product was sampled, and the crystal structure was identified by X-ray and the density was measured by Archimedes method. The results are shown in Table 1.

What is characteristic in the X-ray analysis results is that βSi ₃ N ₄ or β sialon peak (A in the table) Y _0.54 (Si _9.57 Al _2.43 ) (O _0.81 N _15.19 ) When comparing the heights of the peaks (B in the table), A <B in the example and A> B in the comparative example. From this, it can be said that the amount of Y _0.54 (Si _9.57 Al _2.43 ) (O _0.81 N _15.19 ) contributes effectively to the characteristics of the silicon nitride disk. Moreover, the glass phase was not recognized by the result of TEM observation.

  In addition, from the sample manufactured simultaneously with the disk-shaped product, a bending test piece was processed according to JISR1601, and the bending strength was measured. The results are also shown in Table 1.

  Using the silicon nitride disk prepared as described above, the spray stability and the service life were tested while dropping molten copper with a centrifugal sprayer.

  The configuration of the centrifugal sprayer used in this test is as shown in FIG. 2, and copper powder was manufactured according to the flow shown in FIG. That is, a copper raw material is put into the graphite crucible 2, and the graphite crucible 2 around which the coil is wound and the graphite hot water nozzle 4 are heated to 1200 ° C. by high frequency induction heating to melt the copper raw material. The temperature measurement was performed with a thermocouple 8 in contact with the hot water nozzle 4.

  Next, the disk 7 is rotated by the motor 6, and the molten copper 3 is dropped when the disk 7 is heated by the radiation of the hot water nozzle 4. The dropped molten copper 3 scatters from the outer periphery of the disk 7, solidifies to become a spherical copper powder, and is recovered by the powder recovery unit 5.

  In this test, the distance between the hot water nozzle 4 and the disk 7 was 20 mm, the rotation speed of the disk was 70000 rpm, and the inside of the chamber 1 of the centrifugal sprayer was a nitrogen atmosphere of 0.5 atm.

  The spray test results are shown in Table 1. Samples Nos. 1, 2, and 3 of the comparative example dropped molten copper to the center of the disk, and the surrounding 1 mm began to melt, became flat, and the spray direction was not horizontal but angled upward. Sprayed with condition. In this case, since the required spherical copper powder was not obtained, it was determined that “no spraying” was possible at that time (see FIG. 4). Here, the sample No. 1 of the comparative example is equivalent to that described in Patent Document 2 described above.

  On the other hand, in sample Nos. 4, 5 and 6 of the examples, true spherical copper powder having an average particle diameter of 52.3 ± 30 μm was obtained. Since sample No6 of the comparative example was insufficient in strength, it was cracked by the thermal shock after dropping the molten copper.

  The silicon nitride disk of the present invention can be used as a disk used in an apparatus for producing copper powder by centrifugal spraying.

It is a front view which shows one Example of the silicon nitride disk of this invention. It is the schematic which shows the structure of a centrifugal sprayer. It is a flowchart which shows the manufacturing process of the copper powder by the centrifugal sprayer of FIG. It is explanatory drawing which shows the determination method of the spray quality in the centrifugal sprayer of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chamber 2 Graphite crucible 3 Molten copper 4 Hot spring nozzle 5 Powder recovery part 6 Motor 7 Disc 8 Thermocouple

Claims (2)

  A silicon nitride-based disk formed by sintering a composition containing 60 to 80% by mass of silicon nitride, 15 to 24% by mass of aluminum nitride, 2 to 8% by mass of alumina, and 2 to 8% by mass of yttria. The silicon nitride-based disk according to claim 1, wherein the crystalline phase contains Y _0.54 (Si _9.57 Al _2.43 ) (O _0.81 N _15.19 ) and βSi ₃ N ₄ or β sialon.

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