JP2002206105A - Method for manufacturing tantalum powder, tantalum powder, and tantalum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To define prerequisites in the course of manufacture from reduced tantalum powder to sintered compact for obtaining tantalum powder of (80,000 to 250,000) μFV/g CV and to obtain tantalum powder by which high CV of >=(80,000 to 250,000) μFV/g can be finally attained. SOLUTION: The method for manufacturing the tantalum powder has a high-temperature heat treatment step where sodium reduction is applied to potassium fluotantalate and the resultant reduced tantalum powder is subjected to high-temperature heat treatment under inert atmosphere, a low-temperature heat treatment step where the resultant tantalum agglomerate after the high- temperature heat treatment step is pulverized, magnesium is added to the resultant powder, and then low-temperature heat treatment is performed under reduced pressure, and a pickling step where the powder is cleaned with acid solution. In this manufacturing method, the high-temperature heat treatment step is carried out at 1,000 to <1,250 deg.C and the low-temperature heat treatment step is carried out at 700 to 1,000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing tantalum powder, a tantalum powder and a tantalum electrolytic capacitor, and more particularly to a method for obtaining a high-capacity tantalum powder having a specific capacitance of 80,000 to 250,000 .mu.FV / g. Things.

[0002]

2. Description of the Related Art A method for producing tantalum powder for electrolytic capacitors is disclosed in Japanese Patent Publication No. 2-4641. In this production method, potassium fluoride tantalate is reduced with sodium, and the obtained reduced tantalum powder is washed and dried, and then, under reduced pressure, at 1250 ° C. to 1550 ° C.
, Heat-treated at 800 to 1000 ° C. under reduced pressure, and then pickled.

In this manufacturing method, the specific capacitance (CV)
Is a suitable method for producing tantalum powder up to about 15000 μFV / g, but it has been found that it is inappropriate for producing tantalum having a CV of 80,000 μFV / g or more.

That is, in order to produce a tantalum powder having a CV of 80,000 μFV / g or more, basically, the reduced tantalum powder must be fine and have a large surface area. 1250-1550 ° C. for such fine reduced tantalum powder
When the high-temperature heat treatment is performed, the temperature is too high, the agglomeration of the powder particles proceeds appropriately, and the surface area decreases. Also,
The tantalum aggregate after the high-temperature heat treatment becomes hard, and its pulverization becomes difficult. Also, the temperature during the low-temperature heat treatment is still too high for the fine reduced tantalum powder, which may also decrease the surface area for the same reason.

Further, an actual tantalum electrolytic capacitor is:
The obtained tantalum powder was pressed and formed into a compact, which was sintered to form a sintered body.Then, the sintered body was subjected to chemical oxidation treatment to form an anode body, which was impregnated with manganese dioxide, It is produced by coating the surface with carbon. In order to obtain a tantalum electrolytic capacitor having a high CV of 80,000 μFV / g or more, not only the properties of tantalum powder but also
It has been clarified that the sintering conditions are affected by the sintering conditions of the sintered body, but the above-mentioned prior invention does not disclose such knowledge.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a manufacturing condition from a reduced tantalum powder to a sintered body for obtaining a tantalum powder having a CV of 80,000 to 250,000 μFV / g. And finally CV is 80,000 ~
An object is to obtain a tantalum powder capable of achieving a high CV of 250,000 μFV / g or more.

[0007]

Means for Solving the Problems The tantalum powder production method of the present invention comprises a high-temperature heat treatment step in which potassium fluoride tantalate is reduced by sodium and the resulting reduced tantalum powder is subjected to a high-temperature heat treatment in an inert atmosphere. The tantalum aggregate after the process is pulverized, magnesium is added thereto, and a low-temperature heat treatment step of performing low-temperature heat treatment under reduced pressure, and a high-temperature heat treatment Over 1000 ° C and 1250 ° C
At a temperature of less than 700 ° C. to 100 ° C.
It is carried out at a temperature of 0 ° C. In the above-mentioned production method, when potassium fluoride tantalate is reduced with sodium, potassium fluoride tantalate and sodium are each divided into small portions in a molten dilute salt and allowed to react with each other. The amount is always between 40 and 40 of the potassium fluorotantalate charged in the dilute salt.
Preferably it is 1000 times.

[0008] The tantalum powder of the present invention has a specific surface area of 2 obtained by reducing potassium fluorotantalate with sodium.
５5 m ² / g reduced tantalum powder is subjected to high-temperature heat treatment under an inert atmosphere, and then metal magnesium is added thereto, and the resulting tantalum powder is subjected to low-temperature heat treatment under reduced pressure,
This tantalum powder is molded under pressure to a density of 4.5 to 5.0 g.
/ Cm ^{3, and} the formed body is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature, and has a density of 103 to
A sintered body having a density of 115% was obtained.
It is characterized by having a specific capacitance of 80,000 to 250,000 μFV / g, which is formed at 60 ° C. and 10 V according to RC-2361. In addition, the above-mentioned tantalum powder has a compression strength of the sintered body after vacuum sintering that is 3 times lower than that of the compact before vacuum sintering.
Preferably, it is up to 20 times. Further, the tantalum powder of the present invention is obtained by reducing potassium tantalate fluoride with sodium, and then subjecting the reduced tantalum powder having a specific surface area of ^{2 to 5} m ² / g to a high-temperature heat treatment in an inert atmosphere, and then adding metallic magnesium. A tantalum powder obtained by performing a low-temperature heat treatment under reduced pressure to obtain a compact having a density of 4.5 to 5.0 g / cm ³ by press-molding the tantalum powder; Vacuum sintering at a temperature equal to or higher than the temperature to obtain a sintered body having a density of 103 to 115% of the density of the molded body, and the sintered body is formed at 60 ° C. and 10 V according to EIAJ RC-2361. The specific capacitance is 60 ° C,
The specific capacitance of those formed at 10V is 80,000 ~ 250,000μF
V / g, and the specific capacitance at 60 ° C. and 20 V is 70% or more of the specific capacitance at 60 ° C. and 10 V. The tantalum electrolytic capacitor of the present invention is characterized by being obtained from any of the above tantalum powders.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the method for producing a tantalum powder of the present invention, first, potassium fluorotantalate (K ₂ TaF ₇ ) is reduced by reacting with sodium in a molten dilute salt to obtain a reduced tantalum powder. KCl-KF, KCl-N
eutectic salts such as aCl-based salts;
The mixture is heated to 900 ° C. to form a melt, and potassium fluoride tantalate and sodium as a reducing agent are charged into the melt to react them.

In the case where potassium fluoride tantalate is reduced with sodium as described above, these may be added continuously, but particularly, potassium fluoride and sodium are separately added to the molten dilute salt. It is preferable that the components are alternately divided into small portions and then charged to react with each other.
Further, the amount of the diluted salt immediately before the addition of sodium is always 40 to 100% of the potassium fluoride tantalate in the diluted salt.
It is preferably 0 times.

That is, first, potassium fluoride tantalate is added to the molten dilute salt. In this case, the respective amounts are adjusted so that the amount of the dilute salt is 40 to 1000 times the potassium fluoride tantalate. . Then, sodium is added to reduce potassium fluorotantalate. Then, potassium fluoride tantalate is further added. Also in this case, potassium fluoride tantalate is added in such an amount that the amount of dilute salt is 40 to 1000 times the amount of potassium fluoride tantalate. As described above, it is preferable that the amount of the diluted salt immediately before the addition of sodium is always 40 to 1000 times the amount of potassium fluorotantalate.

After completion of the reaction between potassium fluoride and sodium tantalate, the diluted salt is cooled, and the obtained agglomerate is repeatedly washed with water, a weakly acidic aqueous solution or the like to remove the diluted salt, and to reduce the reduced tantalum powder. obtain. In this case, if necessary, separation operations such as centrifugation and filtration may be combined, or the particles may be washed and purified with a solution in which hydrofluoric acid and hydrogen peroxide are dissolved.

As described above, when potassium fluoride tantalate is reduced while adjusting the amount of potassium fluoride tantalate and the amount of diluting salt to produce reduced tantalum powder, the obtained powder becomes finer and high CV is obtained. Achievable tantalum powder. The amount of the diluted salt is 40% of potassium fluorotantalate.
If the ratio is less than twice, the concentration of the starting material potassium fluoride tantalate in the dilute salt is too high, so that the reduction reaction speed is increased, and the particle size of the generated tantalum particles may be too large. On the other hand, when the amount of the dilute salt exceeds 1000 times, the reduction reaction rate decreases, and the productivity decreases. The specific surface area of the reduced tantalum powder thus obtained by the BET method is usually 2
５5 m ² / g.

During the reduction reaction, boron oxide (B ₂ O ₃ ) or potassium boron fluoride (KB)
A boron compound such as F ₄ ) may be added. By adding the boron compound, excessive reduction in the size of the reduced tantalum powder can be suppressed. Here, the addition amount of boron is preferably 5 to 100 ppm based on the tantalum powder. If it is less than 5 ppm, the effect of suppressing fineness is insufficient, while if it exceeds 100 ppm, the movement of the boron oxide through the gas phase during sintering increases, and it may precipitate on the lead wire when it is used as a capacitor. Not preferred.

The obtained reduced tantalum powder is then
High temperature heat treatment in an active atmosphere to cause thermal aggregation and tantalum coagulation
A high-temperature heat treatment step of forming a mass is performed. Where the inert atmosphere
Is an atmosphere of an inert gas such as helium or argon.
Other, reduced pressure atmosphere (10^-3-10 ^-Fourtorr). This
In the high temperature heat treatment step, the reduced tantalum powder is
It is important to heat-treat at a temperature of 1250C or higher and lower than 1250C
It is. Heat treatment at such a temperature allows the
Ultra-fine particles present in iron powder
Secondary particles. Below 1000 ° C
Can sufficiently coagulate the reduced tantalum powder
Absent. On the other hand, when the temperature exceeds 1250 ° C., the powder after thermal aggregation is hardened.
It becomes too crushed to become too crushed and the resulting tan
The surface area of the tall powder is small and high CV cannot be achieved
It becomes a powder. Forming and sintering relatively large secondary particles
The sintered body obtained from the sintered body obtained from ultra-fine particles
Also have large pores, which are used as anode electrodes
The electrolyte solution penetrates into the sintered body,
The capacity can be increased. The details will be described later.
However, the high-temperature heat treatment temperature here is 1000 ° C. or more and 12
Sintering at the time of manufacturing a tantalum sintered body at less than 50 ° C
The temperature is from 1000 ° C. to 1450 ° C., preferably 1150 ° C.
By setting the temperature to 1400 ° C., sufficient strength is obtained.
In addition, a tantalum sintered body having appropriate holes can be manufactured.
The heating time in the high-temperature heat treatment step is usually 15 minutes to 2:00
It is about between.

Prior to this high-temperature heat treatment step, the tantalum powder is vibrated using a centrifuge or the like.
A preliminary coagulation step of adding water in such an amount that the entire powder is uniformly wetted may be performed. By performing this preliminary aggregation step, a stronger aggregate can be obtained. In addition, the water added in the pre-coagulation step has a metal content of 20 to 400 pp.
By adding phosphorus of m or 5 to 100 ppm of boron in advance, fusion growth of primary particles can be suppressed and thermal aggregation can be performed while maintaining a high surface area. Examples of the form of phosphorus to be added here include phosphoric acid and ammonium phosphate hexafluoride. Examples of the form of boron include boron compounds such as boron oxide (B ₂ O ₃ ) and potassium boron fluoride (KBF ₄ ). In addition,
Phosphorus may be added at any time before pressure molding described below. By adding before pressure molding, excessive progress of sintering to be performed subsequently can be suppressed.

After the cake-like tantalum powder obtained in the high-temperature heat treatment step is crushed in the air or in an inert gas,
Magnesium is added thereto, and the mixture is heated under reduced pressure to perform a low-temperature heat treatment step of reacting oxygen and magnesium in the tantalum particles to remove oxygen. In this low temperature heat treatment step, the tantalum powder to which magnesium is added is
Heat treatment is usually performed at a temperature lower than 0 ° C. for about 2 to 10 hours.
By performing the heat treatment under such conditions, oxygen in the tantalum powder diffuses and moves to the surface, reacts with magnesium to generate magnesium oxide, and most of the oxygen is removed as magnesium oxide. In particular, the temperature is set to 700 ° C. or higher, at which the magnesium chip is melted and the oxide film of tantalum begins to diffuse, and reaches 1000 ° C. or lower, which reaches a high-temperature heat treatment region and in which the surface area is greatly reduced by surface diffusion.

Next, air is gradually introduced into the tantalum powder deoxygenated in the low-temperature heat treatment step to perform a gradual oxidation treatment for forming a stable film on the surface of the tantalum particles.
After that, perform an acid washing step of washing this with an acidic solution,
The remaining substances such as magnesium oxide and magnesium oxide derived from magnesium are removed and dried.

When a tantalum electrolytic capacitor is manufactured using the tantalum powder thus obtained, first, about 1 to 5% by weight of camphor (C ₁₀ H ₁₆ O) or the like is added as a binder. Pressed, density 4.5-
A molded body of 5.0 g / cm ³ is produced. Next, the tantalum compact is heated under a vacuum condition of about 10 ⁻⁴ to 10 ⁻⁶ torr at a temperature equal to or higher than the heating temperature in the high-temperature heat treatment step.
Preferably, the heating temperature is higher than the heating temperature of the high temperature heat treatment step by 0 to 20.
At 0 ° C. higher temperature, that is, about 1000 to 1450 ° C.,
It is sintered for about 0.3 to 1 hour to produce a sintered body. More preferably, it is 1150-1400 degreeC. As described above, the heating temperature of the high temperature heat treatment step is 0 to 200
By sintering at a high temperature, it is possible to produce a tantalum sintered body having sufficient strength and also having appropriate holes.

Here, the density of the sintered body is preferably 103 to 115% of the density of the molded body. 103
%, The strength is insufficient and is not practical. On the other hand, if it exceeds 115%, the volume shrinkage due to sintering is too large, and it is difficult to control the dimensions of the sintered body. By setting the density of the sintered body to 103 to 115% of the density of the molded body, the sintered body suitable for use in a tantalum electrolytic capacitor can be obtained.

Further, the compression strength of the sintered body is preferably 3 to 20 times the compression strength of the molded body. If it is less than three times, the strength is insufficient and it is not practical, and when a tantalum electrolytic capacitor is used, an abnormality may occur. On the other hand, when it exceeds 20 times, the strength is too high and too hard, and the number of pores is small. Therefore, impregnation with manganese oxide becomes insufficient, and it may be difficult to produce a cathode body.

The sintered body obtained in this way is
According to JRC-2361, a tantalum electrolytic capacitor using this sintered body as an anode electrode by forming at 60 ° C. and 10 V has a specific static transfer capacity of 80,000 to 25.
The capacity is as high as 10,000 μFV / g. In addition, EIAJ RC-
2361 is defined as a test method for a tantalum sintered element for an electrolytic capacitor in the standards of the Japan Electronic Machinery Manufacturers Association. The specific capacitance when this sintered body is formed at 60 ° C. and 20 V is preferably 70% or more of the specific capacitance of the product formed at 60 ° C. and 10 V. If this value is less than 70%, there are too few pores of a suitable size suitable for use in the anode electrode, it is difficult to form manganese dioxide for forming the cathode, and impregnation of the electrolyte is insufficient. May be. In addition, there is a variation in the primary particle size constituting the sintered body, and when there are many fine particles whose chemical conversion coating thickness is insufficient when converted at 20 V,
Leakage current may increase due to incomplete conversion film formation as well as CV reduction.

When this sintered body is used as an anode, before the reduced tantalum powder is pressed,
The lead wire is embedded in the powder, pressed, sintered, and integrated. This is formed into an anode electrode. As the formation conditions, for example, a temperature of 30
At a current density of 30 to 120 mA / g in an electrolytic solution of phosphoric acid, nitric acid,
Conditions for boosting to 60V and treating for 1 to 3 hours can be exemplified. Specifically, manganese dioxide, a solid electrolyte layer such as lead oxide or a conductive polymer, a graphite layer, and a silver paste layer are sequentially formed on the sintered body by a known method, and then a cathode terminal is formed thereon. After connection by soldering or the like, a resin jacket is formed and used as an anode electrode for a solid electrolytic capacitor.

In such a tantalum powder, the reduced tantalum powder is subjected to a high-temperature heat treatment at a temperature of 1000 ° C. or more and less than 1250 ° C.
Since it is obtained by performing at a temperature of 00C to 1000C, it is a fine reduced tantalum powder having a large surface area,
And it is not excessively aggregated and has a surface area of ^{2 to 5} m ² / g.
Degree and high surface area. Therefore, it is suitable for use as an anode electrode of a tantalum electrolytic capacitor. In the case of producing reduced tantalum powder, potassium and sodium fluoride tantalate are each divided into small portions in a molten dilute salt, and are charged and allowed to react with each other. 40-1 of potassium acid
By setting the ratio to 000, a finer reduced tantalum powder suitable for use as the anode electrode of a tantalum electrolytic capacitor can be obtained.

When such a tantalum powder is subjected to pressure molding and further vacuum sintering to form a sintered body, the density of the compact is 4.5 to 5.1 g / cm ³ , and By setting the density of the sintered body to 103 to 115% of the density of the molded body, the sintered body has excellent strength and is easy to control the size, and is a sintered body suitable for use in a tantalum electrolytic capacitor. Further, by setting the compressive strength of the sintered body to 3 to 20 times the strength of the molded body before vacuum sintering, it becomes more practical. By using such a sintered body, it can be converted to 60 according to EIAJ RC-2361.
The specific static transfer capacity when formed at 10 ° C. and 10 V is as high as 80,000 to 250,000 μFV / g.
The specific capacitance when formed at 0 ° C. and 20 V is 60 ° C.
It becomes 70% or more of the specific capacitance of the material formed at 10 V, and has an appropriate size of pores suitable for use as an anode electrode.

[0026]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to examples. [Example 1] 200 kg of a mixture of potassium fluoride and potassium chloride as a diluting salt was placed in a nickel reactor equipped with a lid, a stirring rod, a sodium inlet, a raw material inlet, an argon gas inlet, and an outlet. The temperature was raised to 830 ° C. to melt. Next, potassium and sodium fluoride tantalate were alternately and subdivided and charged into the reactor. At this time, immediately before the addition of sodium, the amount of the diluted salt was adjusted to be 80 to 120 times the amount of potassium fluorotantalate. The total amount of potassium fluoride tantalate was 40 kg, and the total amount of sodium was 12 kg. After the completion of the reduction reaction, the mixture was cooled, and the obtained agglomerates were crushed and washed with a weakly acidic aqueous solution to obtain reduced tantalum particles. Further, purification was performed using a cleaning solution containing hydrofluoric acid and hydrogen peroxide.
Table 1 shows the surface area and the elemental analysis results of the tantalum particles thus obtained by the BET method.

Next, phosphorus is added to the reduced tantalum powder in an amount of 1%.
After adding phosphoric acid to 50 ppm, this was put in a bowl and filled with water. Then, this was put into the pot of the centrifugal dehydrator with the filter paper attached. After dehydration for a predetermined time, the water content was measured and found to be 5 wt%. The dehydrated tantalum powder was spread on a tray and allowed to stand, and was naturally dried (preliminary aggregation). Then, this was placed in a heating furnace and heated at 1200 ° C. for 0.5 hour under reduced pressure (10 ⁻⁴ torr) to perform a high-temperature heat treatment step to cause thermal aggregation. Then, the aggregate that had been thermally agglomerated was crushed and passed through a sieve having openings of 250 μm. 5% by weight of magnesium chips is added to the pulverized material (tantalum).
After holding for a long time, a low-temperature heat treatment step was performed to perform deoxidation in which oxygen in the tantalum reacted with magnesium. And
In the subsequent cooling process, air was introduced into the argon gas to perform a slow oxidation stabilization treatment on the tantalum powder, and the powder was taken out of the furnace.
Next, the powder thus taken out was washed with a nitric acid solution, and magnesium and magnesium oxide were washed and removed. Physical properties and elemental analysis of the obtained tantalum powder were as shown in Table 2.

This powder was molded under pressure to a density of 4.5 g /
A molded body having a size of ³ cm ³ was vacuum-sintered (10 ⁻⁵ torr) at 1300 ° C. for 20 minutes to produce a sintered body. With respect to the molded body and the sintered body, the molded body density, the molded body strength (compression strength), the sintered body density, and the sintered body strength (compression strength) were measured. Table 3 shows the results.

Further, the obtained sintered body was formed in a 1% phosphoric acid aqueous solution at 60 ° C. at a formation voltage of 10 V, and then formed at 25 ° C.
CV measurement was performed in a 30% aqueous sulfuric acid solution. Similarly, after forming at a formation voltage of 20 V, CV measurement was performed. The formation current density was 90 mA / g. Table 4 also shows these results.

Example 2 Using the same reactor as in Example 1, 400 kg of a mixture of potassium fluoride and potassium chloride was added as a diluting salt, and KBF ₄ was added as a refining agent in an amount of 20 kg.
g was added and the temperature was raised to 830 ° C. to melt. Then, potassium fluoride and sodium fluoride tantalate were alternately divided into small portions and charged into the reaction vessel. At this time, immediately before the addition of sodium, the amount of the diluted salt was always 200 to 400 times the amount of potassium fluorotantalate. In addition,
The total charge of potassium fluorotantalate was 40 kg and the total charge of sodium was 12 kg. After the completion of the reduction reaction, the mixture was cooled, and the obtained agglomerates were crushed and washed with a weakly acidic aqueous solution to obtain reduced tantalum particles. Further, purification was performed using a cleaning solution containing hydrofluoric acid and hydrogen peroxide. Table 1 shows the surface area and the elemental analysis results of the tantalum particles thus obtained by the BET method.

Next, phosphorus is added to the reduced tantalum powder by 3%.
After adding phosphoric acid so as to be 00 ppm, this was put in a ball and filled with water. Then, this was put into the pot of the centrifugal dehydrator with the filter paper attached. After dehydration for a predetermined time, the water content was measured and found to be 5 wt%. The dehydrated tantalum powder was spread on a tray and allowed to stand, and was naturally dried (preliminary aggregation). Then, this was placed in a heating furnace and heated at 1200 ° C. for 0.5 hour under reduced pressure (10 ⁻⁴ torr) to perform a high-temperature heat treatment step to cause thermal aggregation. Then, the aggregate that had been thermally agglomerated was crushed and passed through a sieve having openings of 250 μm. 5% by weight of magnesium chips is added to the pulverized material (tantalum).
After holding for a long time, a low-temperature heat treatment step was performed to perform deoxidation in which oxygen in the tantalum reacted with magnesium. And
In the subsequent cooling process, air was introduced into the argon gas to perform a slow oxidation stabilization treatment on the tantalum powder, and the powder was taken out of the furnace.
Next, the powder thus taken out was washed with a nitric acid solution, and magnesium and magnesium oxide were washed and removed. Physical properties and elemental analysis of the obtained tantalum powder were as shown in Table 2.

This powder was molded under pressure to a density of 4.5 g /
A molded body having a size of ³ cm ³ was vacuum-sintered (10 ⁻⁵ torr) at 1300 ° C. for 20 minutes to produce a sintered body. With respect to the molded body and the sintered body, the molded body density, the molded body strength (compression strength), the sintered body density, and the sintered body strength (compression strength) were measured. Table 3 shows the results.

Further, the obtained sintered body was formed in a 1% phosphoric acid aqueous solution at 60 ° C. at a formation voltage of 10 V.
CV measurement was performed in a 30% aqueous sulfuric acid solution. Similarly, after forming at a formation voltage of 20 V, CV measurement was performed. The formation current density was 90 mA / g. Table 4 also shows these results.

In Examples 1 and 2, the strength of the compact and sintered compact was 150 mg of tantalum powder having a diameter of 3 m.
m using a pellet formed into a pellet, and applying a load in the diameter direction of the pellet, the load when a crack occurs in the pellet,
Expressed as strength.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

As described above, as shown in Tables 1 to 4, the tantalum powder obtained in the present embodiment has the optimum strength for use in a tantalum electrolytic capacitor and has a high CV (80,000 to 2
It was possible to produce a pellet achieving 50,000 μFV / g). Further, when the tantalum powder of the present embodiment is used,
The density of the sintered body with respect to the density of the compact is in the range of 103 to 115%, and the density of the sintered body with respect to the strength of the compact is 3%.
２０20 times, and 2 times the CV value at 10V.
The CV value at 0 V was 70% or more.

[0040]

As described above, the tantalum powder of the present invention is obtained by subjecting reduced tantalum powder to a high temperature heat treatment step.
Since it is obtained by performing the low-temperature heat treatment step at a temperature of 700 ° C. to 1000 ° C. at a temperature of at least 00 ° C. and less than 1250 ° C., it is a fine reduced tantalum powder having a large surface area and excessively agglomerated. And surface area 2-5
The surface area is as high as about m ² / g. Therefore, CV is 80,000 ~
A 250,000 μFV / g tantalum electrolytic capacitor can be manufactured. Further, according to the production method of the present invention, a tantalum powder capable of achieving a high CV of 80 to 250,000 μFV / g or more can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K017 AA01 BA07 DA08 EH01 4K018 BC01 DA32 KA39

Claims (7)

[Claims] 1. A high-temperature heat treatment step in which potassium fluoride tantalate is sodium-reduced, and the obtained reduced tantalum powder is subjected to high-temperature heat treatment in an inert atmosphere, and a tantalum aggregate after the high-temperature heat treatment step is pulverized, and magnesium is added thereto. In a method of producing a tantalum powder having a low-temperature heat treatment step of performing low-temperature heat treatment under reduced pressure and a pickling step of washing the same with an acidic solution, the high-temperature heat treatment step is performed at a temperature of 1000 ° C. or more and less than 1250 ° C. A method for producing a tantalum powder, wherein the low-temperature heat treatment step is performed at a temperature of 700C to 1000C. 2. When reducing potassium fluoride tantalate with sodium, potassium fluoride tantalate and sodium are each divided into small portions in a molten dilute salt and allowed to react with each other. The amount is always between 40 and 100 of the potassium fluorotantalate charged in the dilute salt.
2. The method for producing tantalum powder according to claim 1, wherein the ratio is 0 times. 3. The reduced tantalum powder has a specific surface area of 2 to 5 m.
The method for producing tantalum powder according to claim 1 or 2, which is ² / g. 4. A reduced tantalum powder having a specific surface area of ^{2 to 5} m ² / g, obtained by reducing potassium fluorotantalate with sodium, is subjected to high-temperature heat treatment in an inert atmosphere, followed by addition of metallic magnesium and reduced pressure. Is a tantalum powder obtained by performing a low-temperature heat treatment at a pressure of 4.5 to 5.0 g.
/ Cm ^{3, and} the formed body is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature, and has a density of 103 to
A sintered body having a density of 115% was obtained.
A tantalum powder characterized by having a specific capacitance of 80,000 to 250,000 [mu] FV / g, which is formed at 60 [deg.] C. and 10 V in accordance with RC-2361. 5. A reduced tantalum powder having a specific surface area of ^{2 to 5} m ² / g, obtained by reducing potassium fluorotantalate with sodium, is subjected to a high-temperature heat treatment in an inert atmosphere, and then metallic magnesium is added thereto. Is a tantalum powder obtained by performing a low-temperature heat treatment at a pressure of 4.5 to 5.0 g.
/ Cm ^{3, and} the formed body is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature, and has a density of 103 to
When the sintered body has a density of 115%, the compressive strength of the sintered body after vacuum sintering is 3 to 2 times the compressive strength of the compact before vacuum sintering.
The tantalum powder according to claim 4, wherein the tantalum powder becomes 0 times. 6. A reduced tantalum powder having a specific surface area of ^{2 to 5} m ² / g, obtained by reducing potassium fluorotantalate with sodium, is subjected to a high-temperature heat treatment in an inert atmosphere, followed by addition of metallic magnesium and reduced pressure. Is a tantalum powder obtained by performing a low-temperature heat treatment at a pressure of 4.5 to 5.0 g.
/ Cm ^{3, and} the formed body is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature, and has a density of 103 to
A sintered body having a density of 115% was obtained.
According to RC-2361, the specific capacitance of the product formed at 60 ° C. and 10 V is 80,000 to 250,000 μFV / g, and the specific capacitance of the product formed at 60 ° C. and 20 V is 60.
A tantalum powder characterized by having a specific capacitance of 70% or more of that formed at 10 ° C. 7. A tantalum electrolytic capacitor obtained from the tantalum powder according to claim 4. Description: