JP2006336042A - Metal powder, and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide metal powder composed of tantalum or niobium which has the compatibility of sinterability and fluidity, and to provide a method for producing the same. <P>SOLUTION: The method for producing metal powder comprises: a thermal flocculation stage where raw material powder composed of tantalum or niobium is subjected to thermal flocculation to obtain flocculated powder; and a cracking stage where the flocculated powder is cracked by a cracking machine (roll granulator 20) provided with differential rolls 21. The metal powder is composed of tantalum or niobium, and multiface grains, wherein flat faces are formed at three or more positions on the surface and the ratio of the flat faces is 30 to 70% of the whole surface area. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal powder comprising tantalum or niobium and a method for producing the same.

Tantalum powder or niobium powder is widely used as a material for anode electrodes of solid electrolytic capacitors. In order to produce tantalum powder and niobium powder for anode electrodes of solid electrolytic capacitors, for example, first, tantalum salt or niobium salt is sodium-reduced in diluted salt, or tantalum chloride or niobium chloride is reduced with hydrogen. A tantalum fine powder or a niobium fine powder is obtained by a method such as Next, the tantalum fine powder or niobium fine powder is granulated with a bread type granulator or the like as a raw material powder to form a granulated powder, the granulated powder is thermally agglomerated, and the agglomerated powder obtained thereby is Grind with a crusher such as a chopper mill. Next, the pulverized powder obtained by the pulverization is sieved to recover a powder having a predetermined particle size range, which is used as a product (see, for example, Patent Document 1).
JP-A-4-362101

The tantalum powder and niobium powder obtained by the conventional manufacturing method have many irregularities formed on the surface and a large difference in the height of the irregularities. The powder having such a shape has a problem that the flow area is low because the contact area between the powders is large and the sinterability required for the powder for the anode electrode can be secured, but the flow resistance is large. .
On the other hand, in order to improve fluidity, it is conceivable to use a substantially spherical powder. In this case, however, the contact area between the powders decreases, so that the sinterability decreases. That is, conventionally, it has been difficult to obtain tantalum powder and niobium powder having both sinterability and fluidity.
This invention is made | formed in view of the said situation, and it aims at providing the metal powder which consists of a tantalum or niobium which was compatible in sinterability and fluidity | liquidity, and its manufacturing method.

The method for producing a metal powder of the present invention includes a thermal aggregation step of thermally aggregating raw material powder made of tantalum or niobium to obtain an aggregated powder,
A crushing step of crushing the agglomerated powder with a crusher equipped with a differential roll.
In the manufacturing method of the metal powder of this invention, you may have the preliminary pulverization process of pre-pulverizing agglomerated powder before a crushing process.
In the metal powder production method of the present invention, the raw material powder is a pulverized raw material powder obtained by compression-molding tantalum fine powder or niobium fine powder and pulverizing with a pulverizer equipped with a differential roll. May be.
The metal powder of the present invention is made of tantalum or niobium, and is characterized in that it is a polyhedral particle having three or more flat surfaces formed on the surface, and the ratio of the flat surfaces is 30 to 70% of the total surface area.

According to the method for producing a metal powder of the present invention, a metal powder made of tantalum or niobium having both sinterability and fluidity can be produced.
The metal powder of the present invention is made of tantalum or niobium and has both sinterability and fluidity.

An embodiment of the method for producing a metal powder of the present invention will be described.
The method for producing the metal powder of the present embodiment includes a thermal aggregation step of thermally aggregating raw material powder made of tantalum (hereinafter referred to as tantalum raw material powder) to obtain an agglomerated powder, a preliminary pulverization step of pre-pulverizing the agglomerated powder, It is a method having a pulverization step of pulverizing the pulverized powder obtained by preliminary pulverization, and a recovery step of sieving the pulverized powder obtained in the pulverization step and collecting powder in a predetermined particle size range .
Hereinafter, each step will be described in detail.

Examples of the thermal aggregation method in the thermal aggregation process include a method of heating tantalum raw material powder in a heating furnace. The heat aggregation temperature is preferably 900 to 1200 ° C, more preferably about 1050 ° C.
It is preferable to obtain an agglomerated powder of 45 to 5000 μm by this thermal agglomeration step. Further, since preliminary pulverization can be simplified or omitted, it is more preferable to obtain an agglomerated powder of 45 to 3000 μm.

  As the tantalum raw material powder, for example, tantalum fine powder of about 3 to 5 μm obtained by sodium reduction of tantalum salt such as sodium fluorinated tantalate in diluted salt, and 3 to 5 μm of tantalum oxide are reduced with a solid reducing agent. Examples thereof include fine tantalum powder obtained as described above. Further, the tantalum raw material powder may be preliminarily heat-aggregated or may be granulated powder by granulating water as a binder.

In addition, as the tantalum raw material powder, after compacting tantalum fine powder to obtain a compact, the compact is crushed by the same pulverizer as that used in the pulverization step. Raw material powder may be sufficient. If the pulverized raw material powder is used as the raw material powder, the preliminary pulverization can be simplified or omitted to obtain the target particle size range, and the number of rolls used in the pulverization step can be reduced.
In the compression molding at that time, for example, a known method using a press apparatus can be adopted.
As a pressing device, for example, as shown in FIG. 1, a rectangular mold 11 in which a through hole 11 a having a circular cross section is formed in the vertical direction, and a cylindrical shape inserted into the through hole 11 a of the mold 11 from below. And a pressing device 10 including a cylindrical pressure body 13 inserted into the through hole 11a of the mold 11 from above. In the press device 10, the inner diameter of the through hole 11a and the outer diameters of the support body 12 and the pressure body 13 are substantially equal.
In the compression molding using this press apparatus 10, as shown in FIG. 2, first, the support body 12 is raised, and the support body 12 is inserted slightly below the through hole 11a of the mold 11 to form a cylindrical shape. Form a mold. Next, as shown in FIG. 3, after filling a predetermined amount of fine tantalum powder 14 from the upper side of the through hole 11a, the pressurizing body 13 is lowered and inserted into the through hole 11a as shown in FIG. A compact is obtained by compression molding the fine tantalum powder 14 filled in 11a. The molded body is lowered by the support body 12 and then protruded by the pressure body 13, or the pressure body 13 is raised and then protruded by the support body 12 and taken out from the mold 11.
In compression molding, the bulk density of the obtained molded body is preferably about 4 to 5 g / cm ³ .

In the preliminary pulverization step, the agglomerated powder is pulverized by a pulverizer. Examples of the pulverizer include crushing pulverizers such as a chopper mill, a speed mill, a jaw crusher, a cutter mill, and a screen mill.
By this preliminary pulverization step, the agglomerated powder is preferably pulverized to 45 to 5000 μm, more preferably about 45 to 3000 μm.

In the crushing step, the pulverized powder is crushed by a crusher equipped with a differential roll. Examples of the crusher provided with the differential roll include a roll granulator 20 provided with the differential roll 21 in three stages as shown in FIG. Here, with the differential roll 21, two rolls 21a and 21b are arranged at intervals, and these rolls rotate in reverse to each other and have different rotational speeds. Moreover, as shown in FIG. 6, the unevenness | corrugation is formed in each peripheral surface of the rolls 21a and 21b with the same period, and the convex part 21c of one roll 21a is the other of the two rolls 21a and 21b. It arrange | positions so as to oppose the recessed part 21d of the roll 21b.
The difference between the peripheral speeds of the two rolls 21a and 21b in the differential roll 21 is that a powder having a predetermined particle size range is obtained with a higher yield, so that the peripheral speed of one roll 21a is the same as that of the other roll 21b. It is preferably 20% or more faster than the peripheral speed.

  Moreover, in the roll granulator 20, it is preferable that the three-stage differential roll has a narrower interval between the rolls 21a and 21b in order from the top. If the gap between the rolls 21a and 21b is reduced in order from the top of the three-stage differential rolls, the particle size can be gradually reduced, so that the yield of powder in a predetermined particle size range is increased. be able to.

  In the pulverization of the pulverized powder using the roll granulator 20 as described above, the pulverized powder is introduced from the upper inlet 22 using gravity, and the particle diameter is reduced through the differential rolls 21 in order from the top, and the lower part. The crushed powder is discharged from the outlet 23 and transferred to the next step.

  In addition, as a crusher, if it has a differential roll, things other than a roll granulator can also be used, for example, a differential type slit roll is mentioned. The differential type slit roll is one in which two rolls having a smooth peripheral surface are arranged with a gap therebetween and rotate in the opposite directions and have different rotational speeds.

Examples of sieving in the collection step include a method of sieving crushed powder by stacking two sieves having different openings. Here, one of the two sieves passes the powder below the upper limit of the predetermined particle size range, but does not pass the powder exceeding the upper limit of the predetermined particle size range, the other of the predetermined particle size range The powder below the lower limit is passed, but the powder above the lower limit of the predetermined particle size range is not passed. Then, the former sieve is used on the top and the latter on the bottom.
As a sieving method, for example, a vibration method or a circumferential motion method can be applied. Here, the vibration method is a method of moving the stacked sieves up and down, and the circumferential motion method is a method of causing the stacked sieves to circularly move in the horizontal direction. Of these, the circumferential method is preferred because the impact is small, the amount of powder smaller than the predetermined particle size range is reduced, and the noise is low.

  Of the powder outside the predetermined particle size range remaining after the recovery step, powder smaller than the predetermined particle size range is returned to the thermal aggregation step, and powder larger than the predetermined particle size range is returned to the crushing step. Is preferred. Thus, by reusing powder outside the predetermined particle size range, the yield of powder within the predetermined particle size range can be increased.

  In the tantalum powder manufacturing method described above, the tantalum raw material powder is thermally agglomerated, and the pulverized powder that has been preliminarily pulverized is passed between two rolls having different rotational speeds, which are differential rolls. Can be crushed. According to this crushing method, since the pulverized powder can be crushed without giving a strong impact, a flat surface is formed on the surface by the extended force, but flattening is prevented by a differential rolling effect, and the sphere A tantalum powder maintaining a shape close to that can be obtained. The powder having a flat surface formed on the surface has a high sinterability because the contact area between the powders becomes large. In addition, a powder having a shape close to a sphere has high flowability because of low flow resistance. That is, the tantalum powder obtained by the manufacturing method described above has both sinterability and fluidity.

In particular, according to the above production method, it is possible to obtain polyhedral particles having three or more flat surfaces formed on the surface and the ratio of the flat surfaces being 30 to 70% of the total surface area. Here, the flat surface is a surface that has a spherical surface lacking and has a curvature of approximately 0, and has an area of 3 to 10% with respect to the total surface area of the particles. When the ratio of the flat surface is 30% or more, the sinterability is high, and when it is 70% or less, the fluidity is high. In addition, when the curvature is substantially 0 and a surface having an area exceeding 10% with respect to the total surface area of the particles is formed, the fluidity is lowered.
The ratio of the flat surface can be obtained by image analysis of a scanning electron micrograph.

In addition, this invention is not limited to embodiment mentioned above.
For example, in the manufacturing method of the embodiment described above, the preliminary pulverization step is included, but the preliminary pulverization step may be omitted. However, if the preliminary pulverization step is included, the efficiency of the pulverization step is improved.
In the embodiment described above, the differential rolls of the crusher are provided in multiple stages, but may be one stage as long as the particle size of the powder to be crushed is small. However, a multi-stage is preferable because a powder having a predetermined particle size range can be obtained with a high yield.

  Furthermore, in the embodiment described above, the tantalum raw material powder is used as the raw material powder of the aggregated powder, but a raw material powder made of niobium (hereinafter referred to as niobium raw material powder) may be used. Even when niobium raw material powder is used, the same effect as that obtained when tantalum raw material powder is used can be obtained.

Example 1
First, 100 g of tantalum fine powder was thermally aggregated at 1100 ° C. to obtain an aggregated powder, and then the aggregated powder was pre-ground by a chopper mill. Next, the pulverized powder preliminarily pulverized in the pulverization step was pulverized with a roll granulator having three stages of differential rolls having a total length of 100 mm to obtain tantalum powder. Here, in each differential roll, the distance between the first-stage rolls was 0.6 mm, the distance between the second-stage rolls was 0.3 mm, and the distance between the third-stage rolls was 0.2 mm. The peripheral speed of one roll was set to be 30% faster than the peripheral speed of the other roll.

(Comparative Example 1)
Instead of the crushing step in Example 1, a speed mill equipped with a screen with a diameter of 250 mm, a mesh opening of 0.5 mm, and a three-stage cutter was used except that the agglomerated powder was pulverized at a cutter rotation speed of 300 rpm. In the same manner as in Example 1, tantalum powder was obtained.

  About the tantalum powder obtained in Example 1 and Comparative Example 1, the particle size distribution was examined by sieving with 100 mesh (aperture 150 μm) and 400 mesh (aperture 38 μm) sieves. Moreover, the ratio of the flat surface of each tantalum powder was calculated | required from the scanning electron micrograph. The results are shown in Table 1.

The tantalum powder of Example 1 in which the agglomerated powder was crushed by a crusher equipped with a differential roll had a narrow particle size distribution and a flat surface ratio in the range of 30 to 70%.
On the other hand, the tantalum powder of Comparative Example 1 in which the aggregated powder was pulverized by a pulverizer had a wide particle size distribution and the flat surface ratio exceeded 70%.

(Example 2)
100 g of tantalum fine powder obtained by sodium reduction of sodium fluorinated tantalate in molten salt is granulated using water as a binder to obtain a granulated powder, and then the granulated powder is thermally aggregated at 1000 ° C. Thus, agglomerated powder was obtained. Next, in the crushing step, the agglomerated powder was crushed with the same roll granulator as in Example 1 to obtain tantalum powder.

(Comparative Example 2)
A tantalum powder having a 325 mesh pass (particle size of less than 45 μm) was reduced with solid magnesium to obtain a tantalum powder.

(Comparative Example 3)
Instead of the crushing step in Example 2, a tantalum powder was obtained in the same manner as in Example 2 except that the agglomerated powder was pulverized at a cutter rotation speed of 300 rpm using the same speed mill as in Comparative Example 1.

About the tantalum powder obtained in Example 2 and Comparative Examples 2 and 3, fluidity was evaluated in accordance with JIS Z 2505-1960.
Moreover, a pellet having a diameter of 1 mm was formed from 6 mg of tantalum powder, and the pellet was sintered at 1300 ° C. for 20 minutes to obtain a sintered body. And the pull-out strength was measured by applying a load to the sintered body in the radial direction. It can be said that the higher the pull-out strength, the higher the sinterability.
Moreover, the ratio of the flat surface of each tantalum powder was calculated | required from the scanning electron micrograph.
These results are shown in Table 2.

The tantalum powder of Example 2 in which the agglomerated powder was crushed by a pulverizer equipped with a differential roll had a flat surface ratio in the range of 30 to 70% and high fluidity. Moreover, the pull-out strength was high and the sinterability was high.
In contrast, the tantalum powder of Comparative Example 2 obtained by reducing 325 mesh pass tantalum oxide powder with solid magnesium had a flat surface ratio of less than 30% and low sinterability.
Moreover, the ratio of the flat surface of the tantalum powder of Comparative Example 3 in which the agglomerated powder was pulverized by a pulverizer was over 70%, and the fluidity was low.

It is a perspective view which shows an example of the press apparatus used for the compression molding process in one Embodiment of the manufacturing method of the metal powder of this invention. It is sectional drawing which shows 1 process of the compression molding using the press apparatus of FIG. It is sectional drawing which shows 1 process of the compression molding using the press apparatus of FIG. It is sectional drawing which shows 1 process of the compression molding using the press apparatus of FIG. It is a schematic diagram which shows an example of the crusher used for the crushing process in one Embodiment of the manufacturing method of the metal powder of this invention. It is a principal part enlarged view of the crusher of FIG.

Explanation of symbols

  14 fine powder of tantalum, 20 roll granulator (crusher), 21 differential roll

Claims (5)

A thermal aggregation process of thermally aggregating raw material powder made of tantalum or niobium to obtain agglomerated powder;
And a crushing step of crushing the agglomerated powder with a crusher equipped with a differential roll.   The method for producing a metal powder according to claim 1, further comprising a preliminary pulverization step of pre-pulverizing the agglomerated powder before the pulverization step.   The method for producing a metal powder according to claim 1 or 2, wherein the raw material powder is a pulverized raw material powder obtained by compression molding tantalum fine powder or niobium fine powder and pulverizing with a pulverizer equipped with a differential roll. .   A metal powder comprising tantalum or niobium, and having three or more flat surfaces on the surface, and the ratio of the flat surfaces is 30 to 70% of the total surface area.   The metal powder according to claim 4, which is used as an anode electrode material for a capacitor.

Images