JP2007291487A - Tantalum powder and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tantalum powder which is highly handleable, and can surely impart superior performance to a tantalum electrolytic capacitor. <P>SOLUTION: The tantalum powder has a particle diameter D<SB>1</SB>of 0.2 to 1.0 μm, which is measured with an air-permeable type specific surface area measurement instrument, and shows a ratio (D<SB>2</SB>/D<SB>1</SB>) of the above particle diameter D<SB>1</SB>to a particle diameter D<SB>2</SB>of 1.0 to 3.0, which is measured according to ASTM B330-02. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a tantalum powder used for a tantalum electrolytic capacitor and a manufacturing method thereof.

The tantalum electrolytic capacitor includes an anode made of a molded body of tantalum powder, an oxide film that is a dielectric provided by chemical conversion of the anode, and a cathode provided to face the oxide film.
The performance, particularly capacity, of the tantalum electrolytic capacitor is affected by the particle size of the tantalum powder constituting the anode, and the leakage current and equivalent series resistance are affected by the higher order structure of the tantalum powder. Therefore, normally, in order to improve the performance of the tantalum electrolytic capacitor, adjustment is made so that the particle diameter of the tantalum powder falls within a specific range (see, for example, Patent Document 1).
As a method for measuring the particle diameter of the tantalum powder, a method based on ASTM B330-20 is widely used.
Special table 2002-516385 gazette

However, as described in Patent Document 1, in order to improve the performance of the tantalum electrolytic capacitor, the particle size of the tantalum powder measured based on ASTM B330-20 is set in a specific range, but the performance of the tantalum electrolytic capacitor is improved. Sometimes did not increase. Furthermore, depending on the particle size, handling of the tantalum powder becomes difficult, and the performance expected when used as a tantalum electrolytic capacitor may not be exhibited.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tantalum powder capable of reliably producing a tantalum electrolytic capacitor having high handling properties and excellent performance, and a method for producing the same.

  As a result of investigating the reason why the performance of the tantalum electrolytic capacitor is not necessarily improved even if the particle diameter of the tantalum powder is in a specific range, the present inventors are based on ASTM B330-02, which has been conventionally adopted in the particle diameter measurement of the tantalum powder. It has been found that there is a problem in the particle size measurement method. That is, in the particle size measurement method based on ASTM B330-02, the measurement is performed without compressing the powder. Usually, when manufacturing a tantalum electrolytic capacitor, the tantalum powder is compression-molded. We found that the diameter changed. Therefore, even if the particle diameter measured based on ASTM B330-02 is specified, the particle diameter is changed after compression molding, so that the performance as a tantalum electrolytic capacitor is not sufficiently exhibited, or tantalum having low handleability. It has been found that it may be powdered. And based on such knowledge, it further examined and invented the following tantalum powder and its manufacturing method.

[1] particle diameter _{D 1} measured using an air permeability type specific surface area measuring device 0.2 to 1.0 [mu] m, and the particle diameter _{D 2} as measured in accordance with ASTM B330-02 particle diameter _{D 1} tantalum powder wherein a ratio _(D 2 / _{D 1)} is 1.0 to 3.0 with.
[2] A tantalum powder production method for producing the tantalum powder according to [1],
A crushing step of crushing the tantalum agglomerated powder to obtain a crushed powder;
A first re-aggregation step in which the pulverized powder is heated in the presence of an oxygen scavenger and agglomerated to obtain a first re-agglomerated powder;
A first re-pulverization step of pulverizing the first re-agglomerated powder to obtain a first re-pulverized powder;
A second re-aggregation step of heating the first re-pulverized powder in the presence of an oxygen scavenger and agglomerating to obtain a second re-agglomerated powder;
And a second re-pulverization step of pulverizing the second re-agglomerated powder to obtain a second re-pulverized powder.

The tantalum powder of the present invention has high handleability and can reliably produce a tantalum electrolytic capacitor with excellent performance.
According to the method for producing a tantalum powder of the present invention, it is possible to produce a tantalum powder that can reliably produce a tantalum electrolytic capacitor having high handleability and excellent performance.

(Tantalum powder)
Tantalum powder of the present invention, the particle diameter _{D 1} measured using an air permeability type specific surface area measuring device 0.2 to 1.0 [mu] m, preferably 0.2～0.85Myuemu, more preferably 0.2 to 0 .6 μm. The present inventors have investigated, tantalum electrolytic capacitor having a particle diameter D ₁ used the following tantalum powder 1.0μm is improved CV value was found to be improved leakage current and ESR. Further, by the particle size D ₁ is 0.2μm or more, the strength required for tantalum powder is secured, it was found that the handling property becomes high.

Particle diameter D ₁ using an air permeability type specific surface area measuring apparatus obtains powder having a specific surface area S _w a _(cm 2 / ^g) using an air permeability type specific surface area measuring device, the specific surface area S _w, D ₁ = 6 / (ρ · S _w ) It is obtained by substituting into (1) (ρ in formula (1) is the density of metal tantalum; 16.6 g / cm ³ ).
Note that equation (1) has a specific surface area of the volume V = (1/6) · π · D 1 3 and the sphere of the sphere ^{_{S w = π · D 1 2}} / w (w is the tantalum powder mass (g)) And ρ = w / V.

The specific surface area measurement method using an air permeation type specific surface area measuring apparatus is the following formula (representing the relationship between the permeability and the specific surface area of air passing through a sample layer made of powder, assuming that the powder is a spherical particle ( 2) It is a measuring method using (Cozeny-Kerman formula).
As shown in FIG. 1, the air permeation specific surface area measuring apparatus used in this measurement has a tubular cell 11 filled with a sample layer 11a made of a powder sample, a cell 11 and a bottom 12a. A cell mounting portion 12 made of a hole member, a liquid level gauge 13a on which a marked line X and a marked line Y are marked, a water filling pipe 13 which is arranged vertically and filled with water, and an outlet for discharging water 14, a flexible connection pipe 15 that connects the water filling pipe 13 and the discharge port 14, an on-off valve 16 provided in the connection pipe 15, and a container 17 that receives the water discharged from the discharge port 14. This is a measuring device 10. An example of the measuring device 10 is a powder specific surface area measuring device SS-100 manufactured by Shimadzu Corporation.

In Equation (2), S _w is the specific surface area of the tantalum powder, ρ is the density of metal tantalum (16.6 g / cm ³ ), and ΔP ₁ is the pressure of the air that passes through the sample layer 11a (hereinafter referred to as the permeation pressure). ), Μ is the viscosity of the air (0.00018 g / (cm · sec)), A is the cross-sectional area of the sample layer 11a (cross-sectional area of the hole of the cell 11), and t is when water is discharged from the discharge port 14. The time until the water surface falls from the marked line X to the marked line Y, L is the height of the sample layer 11a, Q is the volume of air that passes through the sample layer 11a, ε is the porosity of the sample layer 11a, 1− This is a value obtained by the equation {W / (ρ · A · L)} (W is the mass of the sample layer 11a). In the measurement according to the present invention, ΔP ₁ is adjusted to 200 mmH ₂ O by adjusting the height of the discharge port 14. Moreover, the volume Q of the air which permeate | transmits the sample layer 11a is equal to the volume of the water which flows out from the water filling pipe | tube 13 when a water surface falls from the marked line X to the marked line Y.

In the specific surface area measurement method using an air permeable specific surface area measurement device, first, the cell 11 is filled with tantalum powder and compressed to form the sample layer 11a. The filling mass W of the tantalum powder when forming the sample layer 11a is 16.6 g. Moreover, since measurement accuracy becomes high, it is preferable to compress so that the density of the sample layer 11a may be set to 4.0-4.5 g / cm < ³ >.
Further, with the open / close valve 16 closed, the water filling tube 13 is filled with water so that the water surface is located above the marked line X of the liquid level gauge 13a.
Next, after measuring the height L of the sample layer 11 a, the cell 11 is mounted on the cell mounting portion 12. Next, the on-off valve 16 is opened, water is discharged from the discharge port 14, and air is caused to flow into the water filling tube 13 through the sample layer 11a. Thereby, air is permeate | transmitted to the sample layer 11a in the cell 11, and the time t until the water surface in the liquid level meter 13a falls from the marked line X to the marked line Y is measured.
Then, [rho in Equation _{(2), △ P 1,} A, t, μ, L, Q, by replacing the values of epsilon, obtaining the _{S w.}
In the measurement using the air permeation type specific surface area measuring device, the state of the air flow in the powder is reflected, so the obtained particle diameter D ₁ reflects the structure of the secondary particles and the structure of the tertiary particles. ing.

Moreover, the tantalum powder of the present invention has a ratio (D ₂ / D ₁ ) of the particle diameter D ₂ measured according to ASTM B330-02 and the particle diameter D ₁ of 1.0 to 3.0, It is preferable that it is 1.0-1.6, and it is more preferable that it is 1.0-1.3. As a result of investigation by the present inventors, it was found that when the ratio of D ₂ / D ₁ is 3.0 or less, a tantalum powder capable of reliably producing a tantalum electrolytic capacitor having excellent performance is obtained. The reason why the performance of the tantalum electrolytic capacitor is enhanced with a tantalum powder having a D ₂ / D ₁ ratio of 3.0 or less is considered to be because the structure of secondary particles or tertiary particles is not easily broken during compression.
Note that the ratio D ₂ / D ₁ is never less than 1.0.

Particle diameter _{D 2} as measured in accordance with ASTM B330-02 is a particle diameter determined by using the equation (3) below.
The measuring apparatus for measuring a particle diameter D _2, as shown in FIG. 2, the air supply means 21 such as a pump for supplying air is connected to the blowing means 21 through the first pipe 22a, dry air Connected to the drying means 22 through the second pipe 23a, and connected to the measurement cell 23 through the third pipe 24a and the tubular measurement cell 23 filled with the sample layer 23b. The pressure regulator 25 is connected to the manometer 24 filled with water, the first pipe 22a, and the pressure regulator 25 is connected to the third pipe 24a. A measuring device 20 including a valve 26.

In Equation (3), L is the height of the sample layer 23b, W is the mass of the sample layer 23b, ρ is the density of metal tantalum (16.6 g / cm ³ ), and ΔP ₂ is the air that has passed through the sample layer 23b. Pressure, P is the pressure of the air supplied to the sample layer 23b, and A is the cross-sectional area of the sample layer 23b (the cross-sectional area of the hole of the measurement cell 23).

In the measurement of the particle diameter D ₂ , first, instead of the measurement cell 23, a flow rate calibration cell whose pressure loss is approximated to the measurement cell is attached, air is supplied by the air supply means 21, and the pressure regulating valve 26 The flow rate is adjusted so that bubbles are generated at intervals of 2 to 3 bubbles / second from the tube tip of the pressure regulator 25 by adjusting the degree of opening.
Further, 16.6 g (W) of tantalum powder is filled in the measurement cell 23 to form the sample layer 23b. In forming the sample layer 23b, the first filter paper 23c is filled with tantalum powder, tapped about 2 to 3 times, covered with the second filter paper 23d, and 222N (Newton) = 50 lbf (Lf: weight) with a torque wrench. Pressure).
Next, after measuring the height L of the sample layer 23 b, the flow rate calibration cell is removed and the measurement cell 23 is attached, and air with a pressure P of 50 cmH ₂ O is supplied to the sample layer 23 b of the measurement cell 23.
Then, after the pressure of the air that has passed through the sample layer 23 b is stabilized, the state is maintained for another 5 minutes, and then the pressure ΔP ₂ of the air that has passed through the sample layer 23 b is measured by the manometer 24. Then, D ₂ is obtained by substituting each value of ρ, ΔP ₂ , A, L, and W into Equation (3). Further, the particle diameter D ₂ can be obtained from a correlation diagram between ΔP ₂ and the particle diameter D ₂ attached to the measuring device 20.
In the measurement of the particle diameter D2, since the air flow in the tantalum powder state is reflected, the particle size D ₂ obtained, the structure of the structure and tertiary particles of secondary particles is reflected.

Since the tantalum powder is compressed and pelletized when the tantalum electrolytic capacitor is manufactured, the particle diameter D ₁ obtained by compressing and measuring the tantalum powder in the cell is a particle that matches the actual situation of manufacturing the tantalum electrolytic capacitor. Is the diameter. Therefore, by using the tantalum powder specifying the particle diameters D ₁ and D ₂ / D ₁ measured using an air permeation specific surface area measuring device, a tantalum electrolytic capacitor having excellent performance can be reliably manufactured.
When D ₁ and D ₂ / D ₁ are within the specific range, the performance of the tantalum electrolytic capacitor is enhanced because the oxidation solution easily penetrates during the chemical conversion treatment even after the tantalum powder is compression-molded. This is because the film can be formed uniformly and the leakage current of the tantalum electrolytic capacitor can be reduced. Moreover, it is thought that electrolyte permeates easily and ESR of the tantalum electrolytic capacitor is reduced.

(Method for producing tantalum powder)
Next, an embodiment of a method for producing tantalum powder for obtaining the tantalum powder will be described.
In the method for producing tantalum powder of the present embodiment, first, in the crushing step, the aggregated powder of tantalum is crushed to obtain a crushed powder.
The aggregated powder of tantalum to be crushed in this crushing step is tertiary particles obtained by agglomerating tantalum secondary particles.
Hereinafter, an example of a method for obtaining an aggregated powder of tantalum will be described.

In this example, in order to form tantalum secondary particles for agglomerated powder, a tantalum powder production apparatus 30 (hereinafter, abbreviated as production apparatus 30) shown in FIG. 3 is used. The production apparatus 30 includes a tantalum reactor 31, a stirring means 32 installed in the reactor 31, and a first tantalum fluoride (K ₂ TaF ₇ ) for adding the tantalum fluoride to the reactor 31. An addition means 33, a second addition means 34 for adding a reducing agent into the reactor 31, a third addition means 35 for adding nitrogen into the container 31, and an exhaust pipe 36 It is.

In order to produce tantalum secondary particles, first, a diluted salt is added into the reactor 31, the inside of the reactor 31 is heated to prepare a molten salt 31 a, and nitrogen is added by the third addition means 35. Added. Next, while stirring the reactor 31 with the stirring means 32, tantalum potassium fluoride is added to the molten salt 31a via the first addition means 33 and melted.
Next, while continuing stirring, the reducing agent is added to the potassium tantalum fluoride melted in the molten salt 31a by the second addition means 34, thereby reducing the potassium tantalum fluoride to produce primary particles. And the primary particles are aggregated to obtain tantalum secondary particles. This operation is repeated several tens of times for each appropriate amount.

Examples of the diluted salt constituting the molten salt include potassium chloride (KCl), sodium chloride (NaCl), potassium fluoride (KF), and eutectic salts thereof.
Examples of the reducing agent include alkali metals and alkaline earth metals such as sodium, magnesium and calcium, and hydrides thereof, that is, magnesium hydride and calcium hydride. Among these, sodium is preferable. When sodium is used as the reducing agent, fluorine in sodium tantalum fluoride reacts with sodium to produce sodium fluoride. Since this fluoride is water-soluble, it can be easily removed in a later step.

  The temperature in the reactor 31 is preferably 800 to 900 ° C. If the temperature in the reactor 31 is 800 ° C. or higher, the components in the reactor 31 can be reliably dissolved, and if it is 900 ° C. or lower, self-sintering of the generated tantalum primary particles can be prevented. The coarsening of the produced | generated particle | grains can be prevented.

As a method of aggregating the tantalum secondary particles obtained by the above method, for example, a method of thermally aggregating the tantalum secondary particles is employed.
The heating temperature when the tantalum secondary particles are thermally aggregated is preferably 900 to 1300 ° C. If heating temperature is 900 degreeC or more, it can fully heat-aggregate and generation | occurrence | production of a fine powder can be suppressed, and if heating temperature is 1300 degrees C or less, excessive thermal aggregation can be prevented and coarsening can be prevented.
Further, at the time of thermal aggregation, it is preferable that water is contained as a binder in the tantalum secondary particles, left standing for a while, and the exuded water is removed and then dried.

In the crushing step, the tantalum agglomerated powder obtained as described above is crushed.
Examples of the method for pulverizing the agglomerated powder include a method using a roll granulator equipped with a differential roll. Here, with a differential roll, two rolls are arrange | positioned with a space | interval, these mutually reversely rotate, and the rotation speed differs.
The difference between the peripheral speeds of the two rolls in the differential roll is that 44-150 μm tantalum powder is obtained in a higher yield, so that the peripheral speed of one roll is 20% or more faster than the peripheral speed of the other roll. It is preferable.
Moreover, the method of using a slit roll is also applicable as a crushing method.

  In pulverization, the agglomerated powder is not pulverized to secondary particles, and the obtained pulverized powder is also tertiary particles.

Next, in the first reaggregation step, the pulverized powder is heated and aggregated in the presence of an oxygen scavenger to obtain a first reaggregated powder.
Examples of the oxygen scavenger used in the first reaggregation step include magnesium and calcium, and magnesium is preferably used.
The heating temperature in the first reaggregation step is preferably 700 to 1000 ° C, and more preferably 700 to 870 ° C. If the heating temperature in the first reaggregation step is 700 ° C. or higher, it can be sufficiently reaggregated, and if it is 1000 ° C. or lower, the primary particles can be prevented from becoming coarse. Therefore, if the heating temperature in the _first reaggregation step is 700 to 1000 ° C., the particle diameter D ₁ is 0.2 to 1.0 μm, and (D ₂ / D ₁ ) is 1.0 to 3.0. The tantalum powder can be easily manufactured.

Next, in the first re-pulverization step, the first re-agglomerated powder is crushed to obtain the first re-pulverized powder. The crushing method in that case is the same as the crushing process mentioned above.
Then, after the first re-pulverization step, a second re-aggregation step is performed by heating and aggregating the first re-pulverization powder in the presence of an oxygen scavenger to obtain a second re-aggregation powder. The second reaggregation step is the same method as the first reaggregation step, but conditions such as heating temperature may be changed. Moreover, you may implement the granulation process of granulating water as a binder before each re-aggregation process.
Next, in the second re-pulverization step, the second re-agglomerated powder is crushed to obtain a second re-ground powder, and this second re-ground powder is used as tantalum powder. The second re-crushing step is the same method as the first re-crushing step, but the crushing apparatus may be changed.

In the first re-aggregation step and the second re-aggregation step in the manufacturing method described above, the oxide film formed on the surface of the crushed powder or the first re-pulverized powder is heated in the presence of the oxygen scavenger. Can be exposed to expose the metallic tantalum. In general, since the metal surface has high activity, the crushed powders exposed from the metal or the first re-pulverized powders can be easily and firmly aggregated. In addition, in this aggregation method, the temperature at the time of aggregation can be lowered, so that the primary particles are hardly coarsened.
Further, in the first re-pulverization step and the second re-pulverization step, the tertiary particles can be uniformly made fine while maintaining a strong bond between the secondary particles.
According to the above production method in which re-agglomeration and re-crushing are repeated, the tantalum secondary particles are strongly agglomerated while preventing coarsening of the primary particles, and the tantalum powder having a tertiary particle diameter in a specific range is produced. it can. Specifically, it is possible particle size _{D 1} 0.2 to 1.0 [mu] _m, the D 2 / _{D 1} to obtain a tantalum powder of 1.0 to 3.0.

In addition, the manufacturing method of the tantalum powder of this invention is not limited to embodiment mentioned above. For example, in the embodiment described above, a reducing agent is added to potassium tantalum fluoride melted in a molten salt in order to form tantalum secondary particles, but the gaseous tantalum compound is contacted with the gaseous reducing agent. And tantalum secondary particles may be formed.
As a method for bringing a gaseous reducing agent into contact with a gaseous tantalum compound, for example, a gaseous tantalum compound is placed in a container, and after supplying the gaseous reducing agent to the container, the container is sealed and heated. (Hereinafter, this method is referred to as a gas phase method).
Examples of the gaseous reducing agent include hydrogen, vaporized sodium, vaporized magnesium, and the like.
The temperature at the time of reduction in the gas phase method is preferably 10 to 200 ° C. higher than the boiling point of the tantalum compound. If the temperature at the time of reduction is 10 ° C. or more higher than the boiling point of the tantalum compound, the reaction is easily controlled, and if the temperature is 200 ° C. or less higher than the boiling point of the tantalum compound, particle coarsening can be prevented.

  In the method for producing tantalum powder of the present invention, the second reaggregation step and the second repulverization step may be repeated one or more times.

(Production Example 1)
First, 15 kg each of potassium fluoride and potassium chloride as diluted salts were charged into a 50 L reactor. Subsequently, nitrogen gas heated to 900 ° C. was introduced into the reactor at a flow rate of 3 L / min, and the inside of the reactor was kept in a nitrogen atmosphere. At the same time, the diluted salt was heated to 850 ° C. to obtain a molten salt. Next, 37.5 g of potassium tantalum fluoride was added to the reactor once, and 1 minute later, 10.8 g of dissolved sodium was added and reacted for 3 minutes. This operation was repeated 40 times to carry out a reduction reaction. During this operation, the reactor was maintained in a nitrogen atmosphere and stirred with a stirring blade (stirring blade rotation speed: 150 rpm). Thereby, tantalum secondary particles were obtained.
Next, phosphoric acid was added so that phosphorus was 150 ppm with respect to the tantalum secondary particles, which was then placed in a ball, filled with water to the powder surface, and left for 2 hours. Then, the exuding water was removed, transferred to a flat plate for drying, and steam dried at 140 ° C.
Next, the dried secondary particles were put in a heating furnace, heated at 1150 ° C. for 0.5 hours, and aggregated to obtain aggregated powder.
Next, the agglomerated powder was crushed with a roll granulator equipped with three stages of differential rolls having a total length of 100 mm to obtain crushed powder. 5% by mass of magnesium chips was added to the crushed powder, heated at 700 ° C. under reduced pressure for 4 hours, and re-agglomerated while deoxidizing to obtain a first re-agglomerated powder.
The first re-agglomerated powder was pulverized with the roll granulator to obtain the first re-pulverized powder, and then magnesium chips were added to the first re-pulverized powder, and 790 ° C. under reduced pressure. The mixture was heated for 4 hours and re-agglomerated while deoxidizing to obtain a second re-agglomerated powder. The second re-agglomerated powder was crushed by a slit roll to obtain a tantalum powder made of the second crushed powder.

(Production Example 2)
First, 15 kg each of potassium fluoride and potassium chloride as diluted salts were charged into a 50 L reactor. Subsequently, nitrogen gas was introduced into the reactor at a flow rate of 3 L / min to keep the inside of the reactor in a nitrogen atmosphere. At the same time, the diluted salt was heated to 850 ° C. to obtain a molten salt. Next, 37.5 g of potassium tantalum fluoride was added to the reactor once, and after 1 minute, 10.8 g of dissolved sodium was added and reacted for 6 minutes. This operation was repeated 30 times to carry out a reduction reaction. During this operation, the reactor was maintained in a nitrogen atmosphere and stirred with a stirring blade (stirring blade rotation speed: 150 rpm). Thereby, tantalum secondary particles were obtained.
Next, phosphoric acid was added so that phosphorus was 150 ppm with respect to the tantalum secondary particles, which was then placed in a ball, filled with water to the powder surface, and left for 2 hours. Then, the exuding water was removed, transferred to a flat plate for drying, and steam dried at 140 ° C.
Next, the dried secondary particles were put in a heating furnace, heated at 1200 ° C. for 0.5 hours, and aggregated to obtain aggregated powder.
Next, the agglomerated powder was crushed with a roll granulator equipped with three stages of differential rolls having a total length of 100 mm to obtain crushed powder. A 5% by mass magnesium chip was added to the crushed powder, heated at 870 ° C. for 4 hours under reduced pressure, and re-agglomerated while deoxidizing to obtain a first re-agglomerated powder.
The first re-agglomerated powder was crushed by the roll granulator to obtain the first re-pulverized powder, and then magnesium chips were added and heated at 800 ° C. under reduced pressure for 4 hours to deoxygenate. While reaggregating, a second reagglomerated powder was obtained. The second re-agglomerated powder was crushed by the roll granulator to obtain a tantalum powder made of the second crushed powder.

(Production Example 3)
First, 15 kg each of potassium fluoride and potassium chloride as diluted salts were charged into a 50 L reactor. Subsequently, nitrogen gas was introduced into the reactor at a flow rate of 3 L / min to keep the inside of the reactor in a nitrogen atmosphere. At the same time, the diluted salt was heated to 880 ° C. to obtain a molten salt. Next, 200 g of potassium tantalum fluoride was added into the reactor once, and after 1 minute, 58 g of dissolved sodium was added and reacted for 6 minutes. This operation was repeated 30 times to carry out a reduction reaction. During this operation, the reactor was maintained in a nitrogen atmosphere and stirred with a stirring blade (stirring blade rotation speed: 150 rpm). Thereby, tantalum secondary particles were obtained.
Next, phosphoric acid was added so that phosphorus was 150 ppm with respect to the tantalum secondary particles, which was then placed in a ball, filled with water to the powder surface, and left for 2 hours. Then, the exuding water was removed, transferred to a flat plate for drying, and steam dried at 140 ° C.
Next, the dried secondary particles were put in a heating furnace, heated at 1250 ° C. for 0.5 hours, and aggregated to obtain aggregated powder.
5% by mass of magnesium chips was added to the crushed powder, heated at 800 ° C. under reduced pressure for 4 hours, and re-agglomerated while deoxidizing to obtain a first re-agglomerated powder.
The first re-agglomerated powder was crushed by the roll granulator to obtain the first crushed powder, and then magnesium chips were added, heated at 900 ° C. under reduced pressure for 4 hours, and deoxygenated. Re-aggregation gave a second re-agglomerated powder. The second re-agglomerated powder was crushed by the roll granulator to obtain a tantalum powder made of the second crushed powder.

(Production Example 4)
First, 15 kg each of potassium fluoride and potassium chloride as diluted salts were charged into a 50 L reactor. Subsequently, nitrogen gas was introduced into the reactor at a flow rate of 3 L / min to keep the inside of the reactor in a nitrogen atmosphere. At the same time, the diluted salt was heated to 880 ° C. to obtain a molten salt. Next, 300 g of potassium tantalum fluoride was added to the reactor once, and after 1 minute, 84 g of dissolved sodium was added and reacted for 6 minutes. This operation was repeated 50 times to carry out a reduction reaction. During this operation, the reactor was maintained in a nitrogen atmosphere and stirred with a stirring blade (stirring blade rotation speed: 150 rpm). Thereby, tantalum secondary particles were obtained.
Next, after adding phosphoric acid so that phosphorus becomes 150 ppm with respect to the tantalum secondary particles, the phosphoric acid is put in a ball, and moisture exuded and removed is transferred to a flat plate for drying and steamed at 140 ° C. Dried.
Next, the dried secondary particles were put in a heating furnace, heated at 1250 ° C. for 0.5 hours, and aggregated to obtain aggregated powder.
A 5 mass% magnesium chip was added to the crushed powder, heated at 900 ° C. under reduced pressure for 4 hours, and re-agglomerated while deoxidizing to obtain a first re-agglomerated powder.
The first re-agglomerated powder was crushed by the roll granulator to obtain a tantalum powder.

(Production Example 5)
First, 15 kg each of potassium fluoride and potassium chloride as diluted salts were charged into a 50 L reactor. Subsequently, nitrogen gas was introduced into the reactor at a flow rate of 3 L / min to keep the inside of the reactor in a nitrogen atmosphere. At the same time, the diluted salt was heated to 850 ° C. to obtain a molten salt. Next, 200 g of potassium tantalum fluoride was added into the reactor once, and after 1 minute, 58 g of dissolved sodium was added and reacted for 6 minutes. This operation was repeated 50 times to carry out a reduction reaction. During this operation, the reactor was maintained in a nitrogen atmosphere and stirred with a stirring blade (stirring blade rotation speed: 150 rpm). Thereby, tantalum secondary particles were obtained.
Next, after adding phosphoric acid so that phosphorus becomes 150 ppm with respect to the tantalum secondary particles, the phosphoric acid is put in a ball, and moisture exuded and removed is transferred to a flat plate for drying and steamed at 140 ° C. Dried.
Next, the dried secondary particles were put in a heating furnace, heated at 1250 ° C. for 0.5 hours, and aggregated to obtain aggregated powder.
5% by mass of magnesium chips was added to the crushed powder, heated at 850 ° C. under reduced pressure for 4 hours, and re-agglomerated while deoxidizing to obtain a first re-agglomerated powder.
The first re-agglomerated powder was crushed by the roll granulator to obtain a tantalum powder.

(Production Example 6)
First, 15 kg each of potassium fluoride and potassium chloride as diluted salts were charged into a 50 L reactor. Subsequently, nitrogen gas was introduced into the reactor at a flow rate of 3 L / min to keep the inside of the reactor in a nitrogen atmosphere. At the same time, the diluted salt was heated to 850 ° C. to obtain a molten salt. Next, 300 g of potassium tantalum fluoride was added to the reactor once, and after 1 minute, 84 g of dissolved sodium was added and reacted for 6 minutes. This operation was repeated 50 times to carry out a reduction reaction. During this operation, the reactor was maintained in a nitrogen atmosphere and stirred with a stirring blade (stirring blade rotation speed: 150 rpm). Thereby, tantalum secondary particles were obtained.
Next, after adding phosphoric acid so that phosphorus becomes 150 ppm with respect to the tantalum secondary particles, the phosphoric acid is put in a ball, and moisture exuded and removed is transferred to a flat plate for drying and steamed at 140 ° C. Dried.
Next, the dried secondary particles were put in a heating furnace, heated at 1250 ° C. for 0.5 hours, and aggregated to obtain aggregated powder.
A 5% by mass magnesium chip was added to the crushed powder, heated at 870 ° C. for 4 hours under reduced pressure, and re-agglomerated while deoxidizing to obtain a first re-agglomerated powder.
The first re-agglomerated powder was crushed by the roll granulator to obtain a tantalum powder.

The tantalum powder of Preparation 1-6 were measured and the particle size _{D 1} and the particle diameter _{D 2.} The results are shown in Table 1.

(Measurement method of particle size _{D 1)}
Using a measuring device 10 (Shimadzu milling body specific surface area measuring apparatus) shown in FIG. 1 to determine the specific surface area S _w tantalum powder, the particle diameter D ₁ by substituting a specific surface area S _w in equation (1) Asked.
In the method for measuring the specific surface area, first, 16.6 g (W) of tantalum powder is filled in the cell 11, and the sample layer 11a is compressed so that the density of the sample layer 11a is 4.0 to 4.5 g / cm ^3. Layer 11a was formed.
Further, with the on-off valve 16 closed, the water filling tube 13 was filled with water so that the water surface was positioned above the marked line X of the liquid level gauge 13a.
Next, after measuring the height L of the sample layer 11 a, the cell 11 was mounted on the cell mounting portion 12. Next, the on-off valve 16 is opened, water is discharged from the discharge port 14, and air is caused to flow into the water filling tube 13 through the sample layer 11a. Thereby, air was permeated through the sample layer 11a in the cell 11, and the time t until the water surface in the liquid level gauge 13a dropped from the marked line X to the marked line Y was measured. The amount of water discharged when the water surface drops from the marked line X to the marked line Y is 20 cm ³ , and the volume Q of the air that has passed through the sample layer 11a is 20 cm ³ .
In the formula (2), the density ρ of tantalum: 16.6 g / cm ³ , the permeation pressure ΔP ₁ ; 100 mmH ₂ O, the cross-sectional area A of the sample layer 11a, and the water surface from the marked line X to the marked line Y Time t, air viscosity μ; 0.00018 g / (cm · sec), sample layer 11a height L, air permeation Q: 20 cm ³ , porosity ε; (1- {W / (ρ · A · by replacing the values of L)}), it was determined _{S w.}

(Measurement method of particle size _{D 2)}
It was determined particle diameter D ₂ by using a measuring device 20 shown in FIG.
In the measurement of the particle diameter D ₂ , first, a flow rate calibration cell is attached instead of the measurement cell 23, air is supplied by the air feeding means 21, the degree of opening of the pressure regulating valve 26 is adjusted, and the pressure regulator 25. The flow rate was adjusted so that 2 to 3 bubbles / second were generated from the tube tip.
Further, 16.6 g (W) of tantalum powder is filled in the measurement cell 23 to form the sample layer 23b. In the formation of the sample layer 23b, the first filter paper is filled with tantalum powder, tapped about 2 to 3 times, covered with the second filter paper, and 222 N (Newton) = 50 lbf (Lf: weight pound) with a torque wrench. Was pressurized.
Next, after measuring the height L of the sample layer 23b, the flow rate calibration cell was removed, the measurement cell 23 was attached, and air with a pressure P of 50 cmH ₂ O was supplied to the sample layer 23b of the measurement cell 23.
Then, after the pressure of the air that has passed through the sample layer 23b has retained its status stably further 5 minutes, the pressure △ P ₂ of the air that has passed through the sample layer 23b was determined by manometer 24. Then, to determine the particle size D ₂ by the correlation diagram between accessory has been △ P ₂ and the particle diameter measuring device.

Further, the CV values of the tantalum powders of Production Examples 1 to 6 were measured as follows. The results are shown in Table 1.
(Measurement method of CV value)
A tantalum powder is molded together with a tantalum wire so as to have a density of 4.5 g / cm ³ to produce a pellet. The pellet is placed in a phosphoric acid aqueous solution having a concentration of 0.1% by volume at 60 ° C., a voltage of 10 V, a current Chemical conversion treatment was performed at 90 mA / g. And the CV value was measured at the temperature of 25 degreeC, the frequency of 120 Hz, and the voltage of 1.5V in the sulfuric acid aqueous solution with a density | concentration of 30.5 volume% using the chemical conversion treatment pellet.
Further, using the tantalum powders of Production Examples 1 to 6, chip-type tantalum electrolytic capacitors generally referred to as “A case” composed of pellets of about 5 mm ³ were obtained. The obtained tantalum electrolytic capacitor was evaluated according to the following criteria.
A: Capacitance per capacitor chip volume is large, leakage current and ESR are extremely small, and particularly excellent performance as a tantalum electrolytic capacitor was exhibited. It was easy to handle as tantalum powder, had a compression rate suitable for small pellets, and had sufficient wire pull-out strength.
○: Leakage current and ESR were sufficiently small, and excellent performance as a tantalum electrolytic capacitor was exhibited. Moreover, the tantalum powder is easy to handle and can be easily manufactured.
X: Leakage current and ESR increased when used for small pellets to ensure wire pull-out strength. Moreover, the compression rate of the tantalum powder is low, and it is difficult to manufacture a small chip-type tantalum electrolytic capacitor.

The tantalum powders of Production Examples 1 to 3 having a particle diameter D ₁ of 0.2 to 1.0 μm and D ₂ / D ₁ of 1.0 to 3.0 are excellent in handleability and applied to tantalum electrolytic capacitors. When performing, it showed excellent performance.
Beyond tantalum powder of Production Example 4 particle diameter _{D 1} exceeds the 1.0 _.mu.m, tantalum powder of Production Example 5 to D 2 / _{D 1} exceeds the 3.0, a is 1.0 .mu.m particle diameter _{D 1,} In addition, the tantalum powder of Production Example 6 in which D ₂ / D ₁ exceeded 3.0 had low handleability and low performance when applied to a tantalum electrolytic capacitor.

It is a schematic diagram which shows an example of an air permeation | transmission type specific surface area measuring apparatus. Is a schematic diagram showing an example of a particle diameter measuring apparatus for measuring a particle diameter D _2. It is a schematic diagram which shows an example of the manufacturing apparatus of a tantalum secondary particle.

Explanation of symbols

10 Measuring device (Air-permeable specific surface area measuring device)
DESCRIPTION OF SYMBOLS 11 Cell 11a Sample layer 12 Cell mounting part 13 Water filling pipe 13a Liquid level gauge 14 Outlet 15 Connection pipe 16 On-off valve 17 Container 20 Measuring apparatus 21 Air supply means 22 Drying means 22a First piping 23 Measurement cell 23a Second Pipe 23b Sample layer 24 Manometer 24a Third pipe 25 Pressure regulator 26 Pressure regulating valve 30 Manufacturing device 31 Container 31a Molten salt 32 Stirring means 33 First addition means 34 Second addition means 35 Third addition means 36 Exhaust pipe

Claims (2)

The ratio of the particle diameter _{D 1} measured using an air permeability type specific surface area measuring device 0.2 to 1.0 [mu] m, and a particle diameter _{D 2} as measured in accordance with ASTM B330-02 and the particle diameter _{D 1} tantalum powder _(D 2 / _{D 1)} is characterized in that 1.0 to 3.0. A tantalum powder production method for producing the tantalum powder according to claim 1,
A crushing step of crushing the tantalum agglomerated powder to obtain a crushed powder;
A first re-aggregation step in which the pulverized powder is heated in the presence of an oxygen scavenger and agglomerated to obtain a first re-agglomerated powder;
A first re-pulverization step of pulverizing the first re-agglomerated powder to obtain a first re-pulverized powder;
A second re-aggregation step of heating the first re-pulverized powder in the presence of an oxygen scavenger and agglomerating to obtain a second re-agglomerated powder;
And a second re-pulverization step of pulverizing the second re-agglomerated powder to obtain a second re-pulverized powder.

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