KR100428948B1 - A production method of tungsten nano powder without impurities and its sintered part - Google Patents

Abstract

Provided is a method for producing tungsten nanometal powder, which comprises ultrasonically ball milling tungsten oxide for 10 to 100 hours and hydrogen reducing the tungsten powder thus ground in a temperature range of 650 to 1000 ° C. for 30 minutes to 5 hours. .

In addition, there is provided a method for producing a tungsten sintered compact, wherein the obtained tungsten nanometal powder is molded and sintered at a temperature of 1250 to 1450 ° C.

According to the method of the present invention, since densification of 95% or more is possible at 52% of the compact density, the tungsten nanopowder of the present invention can be applied as a raw powder for powder injection molding for producing a product having a complicated shape. In addition, the nanopowder may be used as a tungsten sintered body for swaging that requires a sintering density of 92 to 94%. Furthermore, since most pores remain at the interface after sintering, the nanopowder is used as a raw material powder for producing the tungsten sintered body for swaging. Extremely preferred.

Description

A production method of tungsten nano powder without impurities and its sintered part}

The present invention relates to a method for producing a tungsten nanometal powder free of impurities as a raw material powder for functional tungsten bulk products. The present invention also relates to a method for producing a sintered body by sintering the tungsten nanometal powder thus prepared at a relatively low temperature.

According to the conventional production method of tungsten raw powder, coarse tungsten powder was molded and sintered at 1250-1400 ° C., and then heated to 2500 ° C. or more by a coolidge method to produce a tungsten sintered body of 90% or more of theoretical density. Since tungsten is a high melting point metal, it is impossible to manufacture a product by a casting process, and heating at 2500 ° C. or more is required for densification of 90% or more of tungsten powder when manufacturing by a sintering process. Therefore, as in this method, the first method of sintering tungsten powder and then using a Coolidge method, which is energized to heat to a temperature of 2500 ° C. or higher, the tungsten sintered body thus produced is generally 92-94% that can be applied to the swaging process. Densification rate is shown. However, because of the need to increase the temperature to a high temperature by the current, a lot of electrical energy is consumed, and thus the manufacturing cost is high.

The method proposed to improve the problems of the prior art as described above is a method of adding a sintering activator to increase the sinterability of the tungsten powder, according to one example of this method, after adding nickel to the coarse tungsten powder to 1% by weight or less , And sintered at a temperature of 1400 ℃ or less to produce a tungsten sintered body of 95% or more. When a small amount of a transition metal such as nickel is added, the tungsten powder exhibits a densification rate of 95% or more at a temperature of 1500 ° C or lower. However, the added nickel forms an alloy phase at the grain boundary of tungsten and lowers the ductility. Therefore, in the swaging process for producing tungsten filament, the tungsten sintered body is destroyed. In addition, nickel causes grain growth of tungsten, which dramatically lowers mechanical properties such as strength.

In a comprehensive review of the prior art, it can be seen that the method of sintering at low temperature without additives is ideal for effectively producing tungsten metal. To this end, it is necessary to maximize the sintering driving force of the tungsten powder. That is, the synthesis of tungsten nanopowders with a maximum specific surface area is required.

Tungsten nanopowders are known to be obtained by reducing tungsten oxide, in which case the particle size of the tungsten nanopowders depends on the pore structure of the oxide agglomerates. The reason for this is that when the water vapor is effectively released through the pores, the partial pressure of tungsten is reduced as the water vapor partial pressure in the reduction reaction region is lowered. Therefore, in general, tungsten oxide powder prepared from tungsten salt having a dense microstructure is difficult to release steam during the hydrogen reduction process, thereby increasing the water vapor partial pressure and causing tungsten grain growth, and thus nano-tungsten powder cannot be prepared. .

Accordingly, the present invention is to provide a method for producing a tungsten nano-powder free of impurities, a method capable of producing a sintered compact close to the perfect densification at a relatively low temperature and a low cost equipment and manufacturing costs by the atmospheric pressure sintering process.

1 is a scanning electron micrograph of the tungsten oxide prepared in Example 1.

2 is a scanning electron micrograph of the tungsten nanometal powder prepared in Example 1.

3 is a graph showing the sintering relative density according to the sintering temperature of Example 1 and Comparative Example 1.

4 is a scanning electron micrograph of a sintered body obtained by sintering the tungsten nanometal powder of Example 1 at 1350 ° C. for 1 hour.

5 is a scanning electron micrograph of a sintered body obtained by sintering the tungsten nanometal powder of Example 1 at 1450 ° C. for 1 hour.

The present invention provides a method for producing a tungsten nanopowder without finely crushed tungsten oxide and hydrogen reduction to avoid the incorporation of impurities.

That is, according to the present invention, tungsten oxide is pulverized without incorporation of impurities using the ultrasonic milling method of the prior patent application of the inventor (Korean Patent Application No. 10-2000-64779), which is an alloy / composite nanometal powder production technology. Specifically, the patent application includes a metal oxide, a ball mill ball media for applying impact and shear forces to the metal oxide, a ball mill solvent for providing fluidity to the metal oxide in one container, and then placing the container in an ultrasonic generator. Pulverizing and mixing the metal oxide by putting an ultrasonic ball mill by vibration of the ball media; A method for producing a high purity alloy and a composite nanometal powder comprising the steps of drying the pulverized mixed metal oxide and then hydrogen reduction is disclosed. Tungsten nano-powder is produced through reduction heat treatment, and the pore amount in the oxide aggregate is increased by the pulverization process by ultrasonic ball milling to effectively release water vapor generated during hydrogen reduction. And the effective vapor release results in lowering the partial pressure of water vapor in the reduction zone, enabling the nanotization of the synthesized tungsten particles.

Tungsten oxide is finely and uniformly crushed by an ultrasonic milling process for 10 to 100 hours. The ground tungsten oxide is hydrogen reduced in a temperature range of 650 to 1000 ° C. for 30 minutes to 5 hours to obtain tungsten nanopowders. If the reduction temperature is less than 650 ℃ the reduction time is increased to increase the productivity, and if it exceeds 1000 ℃ because the particles are grown and aggregated, it is difficult to obtain densified particles due to the sintering driving force in the subsequent sintering process.

In addition, the obtained tungsten nano powder may be sintered in a hydrogen atmosphere of 1250 ~ 1700 ℃ temperature. In this temperature range, the sintered compact densified by 92% or more can be obtained in a short time while making the grain size as small as possible.

<Example>

Hereinafter, the present invention will be described in more detail with reference to examples and drawings, but the present invention is not limited to these examples.

<Example 1>

Blue tungsten oxide having an average particle size of 20 μm was ultrasonically ball milled for 20 hours using the method disclosed in Korean Patent Application No. 10-2000-64779. The vessel of the ultrasonic generator used had a size of 400 mm (width) x 390 mm (width) x 200 mm (height) and the output was 1200 W.

Tungsten oxide powder ball milled by ultrasonication has a form of a sponge cake after drying, which is sieved in a 100 mesh sieve to a powder state. 1 is a photograph observing the shape of the tungsten oxide pulverized in this manner with a scanning electron microscope (magnification: 150,000 times). As shown in the photo, tungsten oxide was successfully crushed to 50 nm or less, and it can be seen that fine particles form fine pores.

Hydrogen reduction of the obtained oxide powder was performed at 800 ° C. for 1 hour to prepare tungsten nanometal powder. The photograph of observing the obtained tungsten nanometal powder with a scanning electron microscope is shown in Figure 1 (magnification: 50,000 times). As a result, tungsten particles of less than 300 nm were observed. The specific surface area of the powder measured using a BET instrument was 4.0 m ² / g. The particle size of tungsten, calculated from this value, was 78 nm. That is, the average particle size of the tungsten nanometal powder observed in the photograph was confirmed to be 78 nm.

The prepared tungsten nanometal powder was made into a cylindrical molded body having a diameter of 15 mm and a height of 10 mm under a pressure of 250 MPa. The molding density at this time was 52%. The obtained molded product was sintered at 1250 to 1450 ° C. for 1 hour in a hydrogen atmosphere.

2 is a graph showing a change in sintered density with temperature. After 1 hour of sintering at 1350 ° C. and 1450 ° C., sintering relative densities of 92% and 95% were shown, respectively.

3 and 4 are photographs of the microstructure of the specimen sintered at 1350 ° C. and 1450 ° C. for 1 hour, respectively, using a scanning electron microscope (magnification: 7,000). The tungsten particle sizes of the specimens sintered at 1350 ° C. and 1450 ° C. were in the range of 2-3 μm and 3-4 μm, respectively, indicating that they were very uniform. In addition, when comparing the sintered relative density and the ratio of pores on the microstructure, most of the pores exist at the interface of the tungsten particles.

Comparative Example 1

Using a tungsten powder having an average particle size of 2.0 μm, a molded body having a relative density of 60% was prepared. The molded product was sintered by maintaining at 1200 ~ 1500 ℃ for 1 hour.

After sintering at 1500 ° C. for 1 hour, the sintered density was only 74% (FIG. 2).

Since the tungsten nanopowder prepared according to the method of the present invention exhibits excellent sintering characteristics that can reach full densification, it is possible to produce a material requiring high specific gravity from pure tungsten. In particular, a tungsten molded body having a molding density of 52% achieved densification close to 95% or more at a low sintering temperature of 1450 ° C. Therefore, the tungsten nanopowder of the present invention having high sintering characteristics is suitable as a raw powder for powder injection molding for producing a product having a complicated shape. In addition, the nanopowder may be used as a tungsten sintered body for swaging that requires a sintering density of 92 to 94%. Furthermore, since most pores remain at the interface after sintering, the nanopowder is used as a raw material powder for producing the tungsten sintered body for swaging. Extremely preferred.

By using the tungsten nanopowder of the present invention, it is possible to manufacture a pure tungsten product having a complicated shape, and it is possible to manufacture a tungsten sintered body for swaging using a simple process condition of low temperature atmospheric pressure sintering at 1450 ° C. and a low cost facility.

In the domestic industrial situation in which the tungsten wire for filament production mainly depends on the import, the production of tungsten nano powder by the technology of the present invention is expected to have a great effect of import substitution.

In addition, the present invention shows that the tungsten nanopowder can be prepared by finely pulverizing pure tungsten oxide and then hydrogen reduction. Therefore, a small amount of impurities of less than 0.1% by weight is mixed, but the oxide can be crushed effectively, so that mechanical methods such as high-energy ball milling used in the production of tungsten-copper nanocomposite powder (Korean Patent Publication No. 97-1558) are pure tungsten nano It can be used for powder production. The powders thus prepared are expected to be used in products that allow a small amount of impurities. For example, there is a product that requires a high specific gravity such as a vibrator of a mobile phone.

Claims (5)

After charging tungsten oxide, a ball mill ball media for applying the impact and shear force to the tungsten oxide, and a ball mill solvent for providing fluidity to the tungsten oxide in one container, the container is placed in an ultrasonic generator for vibration of the ball media. Pulverizing the tungsten oxide by performing an ultrasonic ball mill; Tungsten nanometal powder manufacturing method comprising the step of drying the finely ground tungsten oxide by the ultrasonic ball mill, hydrogen reduction at a temperature range of 650 ~ 1000 ℃. delete delete delete After charging tungsten oxide, a ball mill ball media for applying the impact and shear force to the tungsten oxide, and a ball mill solvent for providing fluidity to the tungsten oxide in one container, the container is placed in an ultrasonic generator for vibration of the ball media. Pulverizing the metal oxide by performing an ultrasonic ball mill; Drying the finely ground tungsten oxide by the ultrasonic ball mill and then performing hydrogen reduction heat treatment at a temperature range of 650 to 1000 ° C .; and Forming the tungsten nano-metal powder formed by the hydrogen reduction heat treatment, and sintering in a hydrogen atmosphere of 1250 ~ 1700 ℃ temperature; manufacturing method of a tungsten sintered body comprising a.