JP2022046953A - W powder - Google Patents

Abstract

To provide a W powder for shaping that is suitable for near net shaping, and resists being flocculated and has favorable flowability, which affects ease of supply and filling.SOLUTION: A W powder has a composition consisting of W and unavoidable impurities. The minimum reflectance measured in the range of 360-740 nm in wavelength is 10% or more. The fluidity measured in accordance with JIS Z 2502 is 15 s/50 g or less. Preferably, the circularity is 0.85 or more; the oxygen content is 0.001-0.020 mass%; and the brightness L* measured in accordance with JIS Z 8781-4: 2013 is 40 or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to W (tungsten) powder suitable for near-net molding such as, for example, a laminated molding method (AM method) and an injection molding method (MIM method).

W, which is a refractory metal, has a low coefficient of thermal expansion and a high thermal conductivity, and is therefore used for electrodes of electronic devices, heating elements of high temperature furnaces, reflectors, and the like. W is also used as a component of X-ray inspection equipment such as a radiation shielding material and a collimator that absorbs scattered radiation because the radiation shielding property in the same volume is superior to that of Pb (lead). ing.
Further, since W has poor machinability, for example, for a complicated shape product such as the collimator, a molded product is produced by near-net molding such as AM method or MIM method in addition to the sintering method using W powder. It is known that a product having a final shape is obtained by subjecting this model to cutting or the like.

Here, since W has a high melting point, it is difficult to obtain the W powder used for the near net molding by the gas atomizing method or the water atomizing method. Therefore, for example, a method for producing W powder using thermal plasma has been proposed in Patent Document 1. In Patent Document 1, a method of generating high-temperature plasma using nitrogen gas under reduced pressure, melting W raw materials with this plasma, and continuously collecting and recovering W ultrafine particles suspended in an atmospheric gas flow is used. It is described and is a useful technique in terms of industrial production scale, that is, it can be produced in large quantities and at low cost.

Japanese Unexamined Patent Publication No. 2-6339

According to the study of the present inventor, it was confirmed that the W powder may be aggregated when the W powder used for the above-mentioned near net molding is to be obtained by the method of Patent Document 1. This problem of agglutination of W powder reduces the fluidity that affects the supplyability and filling property of stably supplying the required amount of W powder to the modeling device and the modeling site during near-net molding, and the product obtained. Higher strength is hindered.

An object of the present invention is to provide a W powder for molding suitable for near-net molding, which suppresses aggregation and has excellent fluidity that affects supplyability and filling property.

The present inventor pays attention to the surface texture to the problem of aggregation of W powder, and by setting the reflectance measured at a specific wavelength within a predetermined range, the supplyability and filling property of W powder are affected. We have found that the fluidity exerted can be greatly improved, and have reached the present invention.

The W powder of the present invention has a composition consisting of W and unavoidable impurities, has a minimum reflectance of 10% or more measured in the wavelength range of 360 to 740 nm, and is measured in accordance with JIS Z 2502. The fluidity is 15 s / 50 g or less.

The W powder of the present invention preferably has a circularity of 0.85 or more.

The W powder of the present invention preferably contains oxygen in the range of 0.001 to 0.020% by mass.

The W powder of the present invention preferably has a brightness L * of 40 or more as measured in accordance with JIS Z 8781-4: 2013.

INDUSTRIAL APPLICABILITY The present invention can provide W powder suitable for near-net molding, which suppresses aggregation and has excellent fluidity that affects supplyability and filling property, and is a technique useful for manufacturing, for example, X-ray inspection equipment. Will be.

A scanning electron micrograph showing the appearance of W powder as an example of the present invention and a comparative example.

The W powder of the present invention has a minimum reflectance of 10% or more measured in the wavelength range of 360 to 740 nm. In the near-net molding such as the AM method and the MIM method described above, an aggregate of powders having a 50% particle size (hereinafter referred to as “D50”) of the volume-based cumulative particle size distribution in the range of 1 to 250 μm is used. Here, the aggregate of W powder for molding containing ultrafine particles having a D50 smaller than 1 μm can be used, for example, for agglomeration of ultrafine particles having a particle size of 0.3 μm or less or molding having a particle size of 1 to 250 μm. Ultrafine particles having a particle size of 0.3 μm or less and agglomerates of ultrafine particles tend to adhere to the surface of the contributing W powder (hereinafter, also referred to as “W powder for molding”). When a large amount of ultrafine particles adhere to the surface of the W powder for molding, a large number of fine irregularities are formed on the surface of the W powder for molding.

The aggregate of W powder for molding having a large amount of ultrafine particles adhered to the surface causes diffuse reflection and absorption of light by the ultrafine particles, and the reflectance is greatly reduced. Therefore, the W powder of the present invention has a minimum reflectance of 10% or more measured in the wavelength range of 360 to 740 nm. As a result, in the W powder of the present invention, the formation of fine irregularities due to the ultrafine particles adhering to the surface of each W powder for molding is suppressed. Therefore, the W powder of the present invention can suppress agglomeration and improve the fluidity that affects the supplyability and the filling property. For the same reason as described above, the minimum value of the reflectance of the W powder according to the embodiment of the present invention is preferably 13% or more, more preferably 13.5% or more.
The reflectance measured in the wavelength range of 360 to 740 nm in the present invention is based on JIS Z 8781-4: 2013, for example, using a spectrophotometer (CM-2500d) manufactured by Konica Minolta. Can be measured.

The W powder of the present invention has a fluidity of 15 s / 50 g or less as measured in accordance with JIS Z 2502. Fluidity is expressed as the time it takes for 50 g of powder to pass through a funnel with a 2.5 mm diameter orifice. The W powder according to the embodiment of the present invention is premised on flowing from the viewpoint of its use, and the fluidity is preferably 14 s / 50 g or less from the viewpoint of stably supplying the required amount of powder to the modeling apparatus at the time of modeling. , 12 s / 50 g or less is more preferable, and 10 s / 50 g or less is further preferable.
In the measurement of fluidity, as described in JIS Z 2502, if the powder does not flow out even if the orifice is opened, the funnel may be lightly tapped once so that the powder flows out.

The W powder according to the embodiment of the present invention may have any shape as long as a predetermined supplyability and filling property can be obtained, and is preferably spherical, specifically, circularity. Is preferably 0.85 or more, and more preferably 0.95 or more.
The circularity referred to in the present invention is calculated by the following mathematical formula, and in the case of a spherical powder, the circularity is 1.0. The higher the circularity is, the more preferable it is from the viewpoint of improving the supplyability and the filling property. ..
[Circularity] = 4π [Projected area of particles] / [Perimeter of particles] ²
Here, for the measurement of the projected area and the perimeter of the particles, for example, an image analyzer can be used.

The W powder according to the embodiment of the present invention preferably contains 0.001 to 0.020% by mass of oxygen. Oxygen may combine with impurities contained in the W powder or W of the base metal to form an oxide. This oxide is taken into the model and remains as a defect, degrading the mechanical properties of the model. Therefore, the W powder according to the embodiment of the present invention preferably has an oxygen content of 0.020% by mass or less.
On the other hand, if the oxygen concentration of the W powder is lower than 0.001% by mass, heat generation due to rapid oxidation may occur when exposed to the atmosphere. Therefore, the W powder according to the embodiment of the present invention preferably has an oxygen content of 0.001% by mass or more.

The W powder according to the embodiment of the present invention preferably has a brightness L * of 40 or more as measured in accordance with JIS Z8781-4: 2013.
In the aggregate of W powder for molding in which a large amount of ultrafine particles are adhered to the surface, diffused reflection and absorption of light by the ultrafine particles occur, and the brightness L * is greatly reduced. Therefore, the W powder of the present invention has a brightness L * of 40 or more. As a result, in the W powder of the present invention, the formation of fine irregularities due to the ultrafine particles adhering to the surface of each W powder is suppressed, the aggregation of the W powder is suppressed, and the supplyability and the filling property can be improved. For the same reason as described above, the brightness L * of the W powder according to the embodiment of the present invention is preferably 45 or more.
The brightness L * referred to in the present invention can be measured by using, for example, a spectrocolorimeter (CM-2500d) manufactured by Konica Minolta in accordance with JIS Z 8781-4: 2013.

In the W powder of the present invention, for example, the W raw material powder obtained by reducing the oxidized W powder or the W raw material powder obtained by cutting and crushing the ingot material is classified into a range of 1 to 250 μm having an appropriate D50 by a near net molding method. W powder can be used. In the present invention, it is preferable to add and mix a flow aid as necessary in order to obtain a W powder having a minimum reflectance of 10% or more measured in the wavelength range of 360 to 740 nm. The flow aid is preferably an alumina or silica powder having a D50 of 1 μm or less, and is preferably added in a range of 50 mass ppm or less.

Further, by performing a spheroidizing treatment on the above W raw material powder using thermal plasma, it is possible to obtain a highly fluid W powder in which aggregation is suppressed. Here, the spheroidizing treatment is a treatment method in which the above-mentioned W raw material powder is passed through a thermal plasma flame and the heat-melted droplets are solidified to obtain spherical W powder. Since the molten droplets solidify in a spheroidized state due to the action of surface tension, it is possible to obtain W powder that is close to a true sphere and has few satellites.
Here, it is preferable to use a mixed gas of hydrogen gas and an inert gas as the operating gas of the thermal plasma flame. By using hydrogen gas as the operating gas, it is possible to generate a thermal plasma flame having a higher energy density, and the melting and spheroidizing of the W raw material powder is promoted. In addition, the oxygen content of W powder can be reduced by the reducing action of hydrogen.

The thermal plasma flame has a temperature distribution and reaches close to 10,000 ° C. in the high temperature region. The W raw material powder that has passed through such a high temperature region not only melts, but a part of it may evaporate, volatilize and gasify, and the particle size having high adhesion when solidifying is 0.3 μm or less. May produce ultrafine particles. The amount of ultrafine particles produced is affected by the state of the thermal plasma flame during the spheroidizing process and the pressure fluctuation in the reactor.
In particular, when the internal pressure of the reactor is reduced during the spheroidizing treatment, the vapor pressure temperature decreases, so that the vaporization of the W raw material powder is promoted and the adhesion of the amount of ultrafine particles to the obtained W powder increases. .. On the other hand, when the internal pressure of the reactor is pressurized during the spheroidizing process, a thermal plasma flame having a higher energy density is formed, and the spheroidization of the W raw material powder is promoted, while the vaporization of W is also promoted. This will increase the adhesion of the amount of ultrafine particles to the obtained W powder. Therefore, when the W powder of the present invention is obtained by a spheroidizing treatment using thermal plasma, the pressure value in the reaction furnace fluctuates (variations) [(maximum value-minimum value) / (maximum value) during the spheroidizing treatment. + Minimum value)] × 100 (%) is preferably adjusted to 5.0% or less.

In addition, the W powder to which a large amount of ultrafine particles are attached has fine irregularities formed on the surface and tends to aggregate, which lowers the fluidity that affects the supplyability and the filling property. Therefore, in order to obtain the W powder of the present invention, it is preferable to use the W powder that has undergone the spheroidizing treatment as the W element powder and remove the ultrafine particles adhering to the surface.
In order to reduce the amount of ultrafine particles adhering to the surface, for example, it is preferable to perform a classification process using an airflow type classifier. In this airflow type classification, for example, by using a precision air classifier and processing the rotor at a rotation speed of 2000 rpm or more, it is possible to reduce ultrafine particles. The rotor rotation speed is preferably 3000 rpm or more, more preferably 4000 rpm or more.

Further, in order to reduce the amount of ultrafine particles adhering to the surface, W elementary powder may be immersed in pure water, alcohol, or the like, and washed by shaking or applying ultrasonic waves. Further, since the ultrafine particles have a high specific surface area and a high oxygen concentration, they may be heat-treated in a reducing atmosphere in which hydrogen is introduced.
In order to obtain the W powder of the present invention, it is not necessary to remove all the ultrafine particles from the surface of the W raw powder, and the minimum value of the reflectance measured in the wavelength range of 360 to 740 nm is 10% or more. As described above, the amount of ultrafine particles adhered may be reduced.

A commercially available W powder was classified and adjusted so that the D50 of the aggregate was 11 μm, and a W raw material powder was prepared. To this W raw material powder, silica powder having a D50 of 1 μm or less as a flow aid is added in a total amount of 30 mass ppm and mixed until the fluidity measured according to JIS Z5052 becomes 15 s / 50 g or less, and the present invention is used. W powder as Example 1 was obtained.

A commercially available W powder was classified and adjusted so that the D50 of the aggregate was 11 μm, and a W raw material powder was prepared. This W raw material powder was spheroidized using a high frequency induced thermal plasma apparatus to obtain W powder having a D50 of 11 μm, which is Example 2 of the present invention.
As the operating conditions, the plasma power was 120 kW, argon (flow rate = 260 L / min) and hydrogen (flow rate = 30 L / min) were adjusted as the operating gas, and argon (flow rate = 8 L / min) was used as the supply gas. At this time, the pressure fluctuation in the reactor during the spheroidizing treatment [(maximum value-minimum value) / (maximum value + minimum value)] × 100 (%) was adjusted to be 2.0%.

A commercially available W powder was classified and adjusted so that the D50 of the aggregate was 11 μm, and a W raw material powder was prepared. This W raw material powder was spheroidized using a high frequency induced thermal plasma apparatus to obtain W raw powder.
As the operating conditions, the plasma power was 120 kW, argon (flow rate = 260 L / min) and hydrogen (flow rate = 30 L / min) were adjusted as the operating gas, and argon (flow rate = 8 L / min) was used as the supply gas. At this time, the pressure fluctuation in the reactor during the spheroidizing treatment [(maximum value-minimum value) / (maximum value + minimum value)] × 100 (%) was adjusted to be 5.6%.
Next, the spheroidized W raw powder was classified using a precision air classifier (TC-25) manufactured by Nisshin Engineering Co., Ltd. at a rotor rotation speed of 4000 rpm, and the D50 was 11 μm. W powder according to Example 3 of the present invention was obtained.

A commercially available W powder was classified and adjusted so that the D50 of the aggregate was 11 μm, and a W raw material powder was prepared. This W raw material powder was spheroidized using a high frequency induced thermal plasma apparatus to obtain W raw powder.
As the operating conditions, the plasma power was 120 kW, argon (flow rate = 260 L / min) and hydrogen (flow rate = 30 L / min) were adjusted as the operating gas, and argon (flow rate = 8 L / min) was used as the supply gas. At this time, the pressure fluctuation in the reactor during the spheroidizing treatment [(maximum value-minimum value) / (maximum value + minimum value)] × 100 (%) was adjusted to be 2.0%.
Next, the spheroidized W raw powder was classified using a precision air classifier (TC-25) manufactured by Nisshin Engineering Co., Ltd. at a rotor rotation speed of 4000 rpm, and the D50 was 11 μm. W powder according to Example 4 of the present invention was obtained.

A commercially available W powder was classified and adjusted so that the D50 of the aggregate was 11 μm, and a W raw material powder was prepared. This W raw material powder was spheroidized using a high frequency induced thermal plasma apparatus to obtain W powder having a D50 of 11 μm as a comparative example.
As the operating conditions, the plasma power was 120 kW, argon (flow rate = 260 L / min) and hydrogen (flow rate = 30 L / min) were adjusted as the operating gas, and argon (flow rate = 8 L / min) was used as the supply gas. At this time, the pressure fluctuation in the reactor during the spheroidizing treatment [(maximum value-minimum value) / (maximum value + minimum value)] × 100 (%) was adjusted to be 5.6%.

For each W powder obtained above, (1) reflectance, (2) fluidity, (3) circularity, (4) oxygen content and (5) brightness L * were measured. The results are shown in Table 1.
(1) Reflectance and (5) Brightness L *
The measurement was performed using a spectrocolorimeter (CM-2500d) manufactured by Konica Minolta in accordance with JIS Z 8781-4: 2013. The reflectance and brightness L * were measured by sandwiching a spacer having a thickness of 1 mm between the detector and the powder sample for measurement in order to suppress the adhesion of the powder to the detector. Further, as the reflectance, the minimum value of the reflectance measured in the wavelength range of 360 to 740 nm was adopted.
(2) Fluidity Measured by a method conforming to JIS Z 2502.
Since the W powder of the present invention Example 2 to the present invention example 4 and the comparative example did not flow out even when the orifice was opened, the measurement was performed after lightly tapping the funnel once so that the powder flowed out.
(3) Circularity It was determined by measuring 20000 pieces using a particle image analyzer (Morphilogi G3) manufactured by Malvern Instruments.
(4) Oxygen content The oxygen content was analyzed by the Infrared gas melting-infrared absorption method.

As shown in FIG. 1, a large number of ultrafine particles (light-colored distribution) having a particle diameter of 0.3 μm or less were observed on the surface of the W powder as a comparative example. Further, in the W powder as a comparative example, it was confirmed that the W powder for molding was agglomerated with each other. Such W powder had a reflectance of less than 10% even when the fluidity was 15 s / 50 g or less. Further, the W powder as a comparative example had an oxygen content of more than 0.020% by mass and a brightness L * of less than 40.

On the other hand, as shown in FIG. 1, it was confirmed that the W powder as an example of the present invention suppressed the adhesion of ultrafine particles having a particle size of 0.3 μm or less. The W powder used as an example of the present invention had a reflectance of 10% or more and a fluidity of 15 s / 50 g or less. In addition, all of the W powders of the present invention have an oxygen content of 0.020% by mass or less, a brightness L * of 40 or more, agglomeration of W powders for molding is suppressed, and supplyability is improved. It was confirmed that the W powder for molding is suitable for near-net molding and has excellent handleability such as filling property.

Claims (4)

It has a composition consisting of W and unavoidable impurities, the minimum reflectance measured in the wavelength range of 360 to 740 nm is 10% or more, and the fluidity measured in accordance with JIS Z 2502 is 15 s / 50 g or less. W powder. The W powder according to claim 1, which has a circularity of 0.85 or more. The W powder according to claim 1 or 2, which contains 0.001 to 0.020% by mass of oxygen. The W powder according to any one of claims 1 to 3, wherein the brightness L * measured in accordance with JIS Z 8781-4: 2013 is 40 or more.

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