WO2002011932A1

WO2002011932A1 - Method for producing tantalum powder, tantalum powder and tantalum electrolytic capacitor

Info

Publication number: WO2002011932A1
Application number: PCT/JP2001/006768
Authority: WO
Inventors: Yujiro Mizusaki; Tomoo Izumi
Original assignee: Cabot Supermetals K.K.
Priority date: 2000-08-09
Filing date: 2001-08-07
Publication date: 2002-02-14
Also published as: JP2002206105A; AU2001276746A1; JP4828016B2

Abstract

A method for producing a tantalum powder, which comprises a high temperature heat treatment step of reducing tantalum potassium fluoride with sodium and subjecting the resultant reduced tantalum powder to a high temperature heat treatment in an inert atmosphere, a low temperature heat treatment step of pulverizing tantalum coagulants from the high temperature heat treatment step, adding magnesium to the resultant powder and subjecting the mixture to a low temperature heat treatment under a reduced pressure, and an acid washing step of washing the product with an acidic solution, wherein the high temperature heat treatment step is carried out at a temperature of 1000 ° or higher and lower than 1250 °, and the low temperature heat treatment step is carried out at a temperature of 700 ° to 1000 °. The method can be employed for producing a tantalum powder having a CV of 80,000 to 250,000 µFV/g, and further allows the production of a tantalum powder having a CV higher than 80,000 to 250,000 νFV/g.

Description

Description Tantalum powder manufacturing method, tantalum powder and tantalum electrolytic capacitor Technical field

The present invention relates to a method for producing tantalum powder, a tantalum powder, and a tantalum electrolytic capacitor, in particular, to obtain a high-capacity tantalum powder having a specific capacitance of 80,000 to 250,000 FV / g. Background art

A method for producing a tantalum powder for an electrolytic capacitor is disclosed in Japanese Patent Publication No. 2-46641.

In this method, potassium tantalum fluoride is reduced with sodium, and the obtained reduced tantalum powder is washed, dried, and then subjected to a high-temperature heat treatment under reduced pressure at 125 ° C. to 150 ° C. In this method, magnesium is added, heat-treated at 800 to 100 ° C under reduced pressure at a low temperature, and pickled.

This method is suitable for producing tantalum powder with a specific capacitance (CV) of up to about 1500 μFV / g, but the CV is 80,000 iFV / g. It turned out to be unsuitable for producing the above tantalum.

That is, in order to produce tantalum powder having a CV of 80,000 μF VZ g or more, the reduced tantalum powder must basically be fine and have a large surface area. If such a fine reduced tantalum powder is subjected to a high-temperature heat treatment at 125 to 150 ° C., the temperature is too high, the agglomeration of the powder particles proceeds moderately, and the surface area decreases. I will. In addition, the tantalum aggregates after the high-temperature heat treatment become hard, and their 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 reduce its surface area for similar reasons.

The actual tantalum electrolytic capacitor is obtained by press-molding the obtained tantalum powder to form a molded body, sintering it into a sintered body, and then subjecting the sintered body to a chemical oxidation treatment to form an anode body. It is manufactured by impregnating this with manganese dioxide and coating the surface with carbon. It has been clarified that obtaining a high CV tantalum electrolytic capacitor of 80,000 μFVZg or more is affected not only by the properties of the tantalum powder but also by the sintering conditions of the sintered body. Does not disclose such findings. Disclosure of the invention

Therefore, an object of the present invention is to clarify the manufacturing requirements from a reduced tantalum powder to a sintered body in order to obtain a tantalum powder having a CV of 80,000 to 250,000 FV / g. An object of the present invention is to provide a tantalum powder capable of achieving a high CV of 80,000 to 257J _β FVZg or more.

The method for producing the tantalum powder of the present invention includes the steps of: reducing potassium tantalum fluoride with sodium; and subjecting the reduced tantalum powder obtained to a high-temperature heat treatment in an inert atmosphere at a high temperature; and pulverizing the tantalum aggregates after the high-temperature heat treatment step. This is a method for producing tantalum powder having a low-temperature heat treatment step in which magnesium is added and a low-temperature heat treatment is performed under reduced pressure, and a pickling step in which the tantalum powder is washed with an acidic solution. Perform at a temperature of less than 1250 ° C and perform the low temperature heat treatment process at a temperature of 700 ° C to 1000 ° C.

In the above-mentioned production method, when reducing tantalum fluoride potassium with sodium, the tantalum fluoride potassium and sodium are each divided into small portions in a molten dilute salt, and they are added to each other to react with each other. It is preferable that the amount is always 40 to 1000 times the amount of tantalum potassium fluoride charged in the diluted salt.

The tantalum powder of the present invention is obtained by subjecting a reduced tantalum powder having a specific surface area of 2 to 5 m2 g obtained by reducing tantalum fluoride with sodium to a high-temperature heat treatment in an inert atmosphere, then adding a metal magnesium, and applying a reduced pressure. Is a tantalum powder obtained by performing a low-temperature heat treatment at a temperature of 4.5 to 5. Og / cm ³ by pressing this tantalum powder into a compact. Vacuum sintering at a temperature of 103 to 115% of the density of the compact was performed, and this sintered compact was formed at 60 ° C and 1 OV according to EIAJ RC-2361. The specific capacitance is between 80,000 and 250,000 FV / g. In the above tantalum powder, the compressive strength of the sintered body after vacuum sintering is preferably 3 to 20 times the compressive strength of the compact before vacuum sintering.

Further, the tantalum powder of the present invention is obtained by subjecting reduced tantalum powder having a specific surface area of 2 to 5 mg obtained by reducing potassium tantalum fluoride with sodium to a high-temperature heat treatment under an inert atmosphere. Then, metal magnesium is added, and tantalum powder is obtained by performing low-temperature heat treatment under reduced pressure. The tantalum powder is pressed and formed to a density of 4.5 to 5.Og / cm ³ . The molded body is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature to form a sintered body having a density of 103 to 115% of the density of the molded body, and this sintered body is EI AJ RC-236. The specific capacitance of the product formed at 60 ° C and 1 OV according to 1 is 60 ° C, the specific capacitance of the product formed at 10V is 80,000 to 250,000 μFV / g, and 60 ° (: The specific capacitance of the product formed at 20V is more than 70% of the specific capacitance of 60 ° C and the product formed at 10V.

The tantalum electrolytic capacitor of the present invention is characterized in that it is obtained from any of the above tantalum powders. 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 tantalum fluoride (K ₂ Ta F ₇ ) is reduced by reacting with sodium in a molten dilute salt to obtain a reduced tantalum powder. Examples of the melt-diluted salt include eutectic salts such as KC 1-KF type and KC 1 _NaC 1 type, and these salts are heated to 800 to 900 ° C. to form a melt. Then, tantalum fluoride and sodium as a reducing agent are charged and reacted.

In the case of reducing the tantalum fluoride steam with sodium as described above, each of these may be added continuously, but particularly, potassium tantalum fluoride and sodium are each added in a small amount to the molten dilute salt. It is preferable that they are alternately divided and charged, and that they react with each other.

Further, 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 tantalum fluoride in the diluted salt.

That is, first, tantalum fluoride fluoride is added to the melt-diluted salt. In this case, the respective amounts are adjusted so that the amount of the diluted salt is 40 to 1000 times the volume of the tantalum fluoride force rim. Next, sodium tantalum is added to reduce potassium tantalum fluoride. Then, potassium tantalum fluoride is further added. Also in this case, the amount of dilute tantalum fluoride is added so as to be 40 to 1000 times the amount of the dilute salt and the tantalum fluoride fluoride. Thus, it is preferable that the amount of the dilute salt immediately before the addition of sodium is always 40 to 100 times the amount of tantalum fluoride lithium.

After the reaction between potassium tantalum fluoride and sodium is completed, 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 obtain a reduced tantalum powder. 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. By reducing the potassium tantalum fluoride while adjusting the amount of the tantalum fluoride roll and the amount of the diluting salt to produce reduced tantalum powder, the resulting powder becomes finer and a high CV can be achieved. It becomes tantalum powder. If the amount of the diluted salt is less than 40 times that of potassium tantalum fluoride, the concentration of the raw material tantalum fluoride roll in the diluted salt is too high, so that the reduction reaction speed is increased, and the particle size of the generated tantalum particles is reduced. May be too large. On the other hand, if the amount of the dilute salt exceeds 1000 times, the reduction reaction rate will decrease, and the productivity will decrease.

The specific surface area of the reduced tantalum powder thus obtained by the BET method is usually 2 to 5 m ² / g. ·

At the time of reduction reaction may be added a boron compound such as boron oxide in the molten diluent salt (B ₂ 0 ₃₎ and boron trifluoride potassium © beam (KBF _4).

By adding a boron compound, excessive reduction in the size of the reduced tantalum powder can be suppressed. The amount of boron added here is preferably 5 to 100 ppm with respect to the tantalum powder. If it is less than 5 ppm, the effect of suppressing the miniaturization is insufficient, while if it exceeds 100 ppm, the movement of the boron oxide through the gas phase during sintering increases, and when it is used as a capacitor, it moves on the lead line. May be undesirably precipitated.

Next, the obtained reduced tantalum powder is subjected to a high-temperature heat treatment in an inert atmosphere to be thermally aggregated, thereby performing a high-temperature heat treatment step of forming a tantalum aggregate. Here, the inert atmosphere includes an inert gas atmosphere such as helium and argon, as well as a reduced-pressure atmosphere (10 · ³ to 10 · ⁴ · rr).

In this high-temperature heat treatment step, it is important that the reduced tantalum powder is heat-treated at a temperature of 100 ° C. or more and less than 125 ° C. By performing the heat treatment at such a temperature, the ultrafine particles present in the tantalum powder can be converted into secondary particles having a relatively large particle diameter. If the temperature is lower than 100 ° C., the reduced tantalum powder cannot be sufficiently heat-agglomerated. Les ,. On the other hand, when the temperature exceeds 125 ° C., the powder after thermal aggregation becomes too hard to be crushed, and the surface area of the obtained tantalum powder becomes small, so that the powder cannot achieve a high CV.

Since the sintered body obtained by molding and sintering relatively large secondary particles has larger pores than the sintered body obtained from ultrafine particles, when this is used as the anode electrode In addition, the electrolyte solution penetrates to the inside of the sintered body, so that high capacity can be achieved. In detail, the force S, which will be described later, and the high-temperature heat treatment temperature here are 100 ° C. or more and less than 125 ° C., and the sintering temperature at the time of manufacturing the tantalum sintered body is 100 ° C. By setting the temperature to 0 ° C to 140 ° C, preferably 115 ° C to 140 ° C, it is possible to obtain a tantalum sintered body having sufficient strength and having appropriate holes. Can be manufactured. The heating time in the high temperature heat treatment step is usually about 15 minutes to 2 hours.

Prior to the high-temperature heat treatment step, a pre-agglomeration step of adding water in such a manner that the whole powder is uniformly wetted may be performed while applying vibration to the tantalum powder using a centrifuge or the like. By performing this preliminary aggregation step, a stronger aggregate can be obtained. In addition, by adding 20 to 400 ppm of phosphorus or 5 to 100 ppm of boron to the metal in advance in the water to be added in the pre-coagulation step, the primary particles can be fused. It suppresses growth and enables thermal coagulation while maintaining a high surface area.

Examples of the form of phosphorus to be added here include phosphoric acid and phosphorus hexafluoride ammonium. The form of boron, boron compounds such as boron oxide (B ₂ 0 ₃₎ and boron trifluoride potassium (KBF ₄₎ and the like. It should be noted that phosphorus may be added at any time before the pressure molding described below. By adding before pressure molding, excessive progress of sintering to be performed 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 to the powder and heated under reduced pressure to react oxygen and magnesium in the tantalum particles with magnesium. A low-temperature heat treatment step of performing deoxidation is performed.

In this low-temperature heat treatment step, the tantalum powder to which magnesium is added is heat-treated at a temperature of less than 700 to 100 ° C., usually for about 2 to 10 hours.

By performing the heat treatment under these 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, when the temperature of the magnesium chip melts, The temperature should be 700 ° C or higher, where the oxide film of the metal starts to diffuse, and 1000 ° C or lower, where the high-temperature heat treatment area is reached and the surface area is greatly reduced due to surface diffusion.

Next, air is gradually introduced into the tantalum powder deoxidized in the low-temperature heat treatment step to perform a slow acid treatment to form a stable film on the surface of the tantalum particles. Thereafter, an acid washing step of washing this with an acidic solution is performed to remove the remaining magnesium oxide and other substances such as magnesium oxide derived from the magnesium, and then dry.

Using the tantalum powder obtained in this way, if you produce a tantalum electrolytic capacitor, first, 1 to about 5 wt% Jiyounou as a binder (C ₁₀ H ₁₆ O) or the like added pressure molding Then, a compact having a density of 4.5 to 5.0 gZ cm ³ is produced.

Then, under vacuum conditions of about the tantalum molded body 10- ⁴ ~10 ^"6 T orr, the heating temperature above the temperature at a high temperature heat treatment step, preferably, by heating the temperature of the high-temperature heat treatment step remote 0 to 200 ° At a high temperature, that is, about 1000 to: 1450 ° C, and sintering by heating for about 0.3 to about! Hours to produce a sintered body, more preferably 1150 to 1400 ° C. In addition, if sintering is performed at a temperature higher by 0 to 200 ° C. than the heating temperature in the high-temperature heat treatment step, a tantalum sintered body having sufficient strength and having appropriate holes can be manufactured. Here, it is preferable that the density of the sintered body is 103 to 115% of the density of the molded body, and if it is less than 103 ° / ₀ , the strength is insufficient and it is not practical. If it exceeds, the volume shrinkage due to sintering is too large and it is difficult to control the dimensions of the sintered body. By the 103-115% of the density, the sintered body suitable for use in tantalum electrolytic capacitors.

Further, the compressive strength of the sintered body is preferably 3 to 20 times the compressive strength of the compact. If it is less than three times, the strength is insufficient and is not practical, and abnormalities may occur when used as a tantalum electrolytic capacitor. On the other hand, if it exceeds 20 times, the strength is too high and too hard, and there are few pores. Therefore, the impregnation of manganese oxide is insufficient, and it may be difficult to manufacture the cathode body.

The tantalum electrolytic capacitor using this sintered body as the anode electrode was formed by forming the thus obtained sintered body at 60 ° C and 10 V in accordance with EIAJ RC-2361. The electric capacity is as high as 80,000 to 250,000 / i FV / g.

Further, the specific capacitance when the 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. This value is 70% If it is less than 100, there are too few pores of a suitable size suitable for use in the anode electrode, so that it is difficult to form manganese dioxide for forming the cathode and impregnation of the electrolyte may be insufficient. You. In addition, if the primary particles that make up the sintered body vary, and there are many fine particles whose chemical conversion film thickness is insufficient when converted at 20 V, not only the CV decreases but also the incomplete conversion Leakage current may increase due to film formation.

In addition, EI AJ RC-2361 stipulates a test method for a tantalum sintered element for an electrolytic capacitor in a standard of the Japan Electronics Machinery Association. In the present invention, the sintered body is formed and the specific capacitance is measured in accordance with EI AJ RC-2361. The specific measuring method is as follows.

First, a lead wire is embedded in the reduced tantalum powder, press-molded, and sintered under the above conditions to produce a sintered body in which the reduced tantalum powder and the lead wire are integrated. Then, the sintered body is heated at a predetermined temperature (for example, a temperature of 30 to 90 ° 〇) in an electrolytic solution such as phosphoric acid or nitric acid having a concentration of about 0.02 to 0.5% by weight at a concentration of 30 to 120 mA / g. After raising the voltage to 10 to 60 V at a current density of 1 to 3 hours, the anode element is subjected to a chemical treatment by holding the voltage for 1 to 3 hours. Next, the formed anode element is washed in pure at 85 ° C, dried, and the specific capacitance is measured. The specific capacitance is 25 ° C and about 30 weight. /. Measure in a sulfuric acid solution with a bias voltage of 1.5 V and a measurement frequency of 120 Hz.

Further, a solid electrolyte layer such as manganese dioxide, 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 to form an anode element. After the cathode terminal is connected to the battery by soldering or the like, a resin jacket can be formed to form a solid electrolytic capacitor.

For such tantalum powder, the high-temperature heat treatment is performed on the reduced tantalum powder at a temperature of 1000 ° C or more and less than 1250 ° C, and the low-temperature heat treatment is performed at a temperature of 700 ° C to 100 ° C. Therefore, it is a fine reduced tantalum powder having a large surface area, is not excessively agglomerated, and has a high surface area of about ^{2 to 5} m ² Zg. Therefore, it is suitable for use as an anode electrode of a tantalum electrolytic capacitor.

Also, when producing reduced tantalum powder, potassium tantalum fluoride and sodium are each divided into small portions and added to the molten dilute salt so that they react with each other. By reducing the size to 40 to 1 000 times the size of the rim, it is possible to use a finer material suitable for use as the anode electrode of tantalum electrolytic capacitors. The original tantalum powder is obtained.

When such a tantalum powder is subjected to pressure molding and further vacuum sintering to obtain a sintered body, the density of the compact is set to 4.5 to 5.0 Og / cm ³ , and the sintering is performed. By setting the density of the green body to 103 to 115% of the density of the green body, the sintered body has excellent strength and good dimensional control, and is suitable for use in tantalum electrolytic capacitors. Become. Furthermore, 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, the specific static transfer capacity when formed at 60 ° C and 10 V in accordance with EIAJRC-2361 is 80,000 to 250,000. / TF V / g, and the specific capacitance when this sintered body is formed at 60 ° C and 20 V is the specific capacitance of that formed at 60 ° C and 10 V. The capacitance becomes 70% or more of the capacitance, and the hole has an appropriate size suitable for use as an anode electrode. Example

Hereinafter, the present invention will be described specifically with reference to examples. Example 1

Place 200 kg of a mixture of potassium fluoride and potassium chloride as a diluting salt in a nickel reactor equipped with a lid, stir bar, sodium inlet, raw material inlet, argon gas inlet, and outlet. The temperature was raised to 30 ° C to melt.

Next, potassium and sodium tantalum fluoride were alternately and subdivided into this reactor. At this time, immediately before the addition of sodium, the amount of the diluted salt was set to be 80 to 120 times that of potassium tantalum fluoride. The total input of potassium tantalum fluoride was 4 O kg and the total input 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, it was purified with a cleaning solution containing hydrofluoric acid and hydrogen peroxide.

Table 1 shows the surface area and elemental analysis results of the tantalum particles thus obtained by the BET method.

Next, phosphoric acid was added to the reduced tantalum powder so that the phosphorous content became 150 ppm, and then the ball was filled with water. And put this in the pot of centrifugal dehydrator The filter paper was attached and charged. 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 coagulation). Then, under reduced pressure was placed in a heating furnace (10- ⁴ To rr), and heated 0.5 h at 1200, subjected to high temperature heat treatment step was heat-aggregated.

Then, the heat-agglomerated nodules were crushed and passed through a sieve with an aperture of 250 μπι. 5% by weight of magnesium chips is added to the ground material (tantalum), kept at 800 ° C for 4 hours under reduced pressure, and subjected to a low-temperature heat treatment step to react oxygen and magnesium in tantalum with deoxygenation. Was done.

Then, during the subsequent cooling process, air was introduced into the argon gas to perform a slow oxidation and stabilization treatment of the tantalum powder, and the powder was taken out of the furnace.

Next, the removed powder was washed with nitric acid water, and magnesium and magnesium oxide were washed and removed.

Table 2 shows the physical properties and elemental analysis of the obtained tantalum powder.

This powder was press-molded density and molding of 4. 5 gZ cm ^3, to produce a sintered body which 1300 ° C, 20 minutes vacuum sintering (10- ⁵ To rr) to.

For the compact and the sintered compact, the compact density, compact strength (compressive strength), compact density, and compact strength (compressive strength) were measured. Table 3 shows the results.

Further, the obtained sintered body was formed in a 0.5% by weight phosphoric acid aqueous solution at 60 ° C at a formation voltage of 10 V, and then subjected to CV measurement in a 30% aqueous sulfuric acid solution at 25 ° C. 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 fluorinated and chlorinated lime was added as a diluting salt, KBF ₄ was added as a finer, and 20 g of kneaded mash was added, followed by heating to 830 ° C. And melted. Next, potassium and sodium tantalum fluoride were alternately divided into small portions and charged into the reaction vessel. At this time, immediately before the addition of sodium, the amount of dilute salt was always 200 to 400 times that of potassium tantalum fluoride. In addition, fluoride The total input of tantalum power rim was 40 kg and the total input of sodium was 12 kg.

After 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, it was purified with a cleaning solution containing hydrofluoric acid and hydrogen peroxide.

Next, phosphoric acid was added to the reduced tantalum powder so that the phosphorous became 300 ppm, and then the ball was filled with water. Then, this was put into a pot of a centrifugal dehydrator with a 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 dry, and this was air-dried (preliminary aggregation). Then, under reduced pressure was placed in a heating furnace (10_ ⁴ To rr), and heated 0.5 h at 1200 ° C, subjected to high temperature heat treatment step was heat-aggregated.

Then, the heat-agglomerated nodules were unframed and passed through a sieve with an aperture of 250 μιη. 5% by weight of magnesium chips is added to the pulverized material (tantalum), kept at 800 ° C for 4 hours under reduced pressure, and subjected to a low-temperature heat treatment step to react oxygen and magnesium in the tantalum with magnesium. Oxygen was performed.

Next, the removed powder was washed with a nitric acid solution, and magnesium and magnesium oxide were washed and removed.

Further, the obtained sintered body was formed in a 0.5% by weight phosphoric acid aqueous solution at 60 ° C at a formation voltage of 10 V, and then subjected to CV measurement in a 30% sulfuric acid aqueous solution at 25 ° C. 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 determined by using 150 mg of tantalum powder formed into a pellet having a diameter of 3 mm, and applying a load in the diameter direction. The load when it occurred was expressed as strength. table 1

Table 2

Table 3 Green body Sintered body

g / cm ³ kg g / cm ³ kg% times

Example 1 4.5 2.8 4.8 28 106.7 10

Execution 2 4.5 2.2 4.8 12.5 106.7 5.7 Table 4

As described above, as shown in Tables 1 to 4, the tantalum powder obtained in the present example has the optimum strength for use in tantalum electrolytic capacitors, and has a high CV (80,000 to 250,000 μFV / g) was able to produce a pellet that achieved.

When the tantalum powder of the present example was used, the sintered body density with respect to the compact density was in the range of 103 to 115%, and the sintered body density with respect to the compact strength was 3 to 20 times. In addition, the CV at 20 V was more than 70% of the CV at 10 V. Industrial applicability

As described above, in the tantalum powder of the present invention, the reduced tantalum powder is subjected to a high-temperature heat treatment step at a temperature of 1000 ° C or more and less than 1250 ° C, and a low-temperature heat treatment step of 700 ° C to 1000 ° C. Since it is obtained by performing at a temperature, it is a fine reduced tantalum powder having a large surface area, is not excessively aggregated, and has a high surface area of about 2 to 5 m ² / g. Therefore, a tantalum electrolytic capacitor with a CV of 80,000 to 250,000 μF VZg can be manufactured.

Further, according to the production method of the present invention, 〇 ¥ is 80000 to 250000 ¥ ^/ _§ more high ¥ a achievable tantalum powder.

Claims

The scope of the claims

1. A high-temperature heat treatment step in which potassium tantalum fluoride is sodium-reduced, and the resulting reduced tantalum powder is heat-treated at a high temperature in an inert atmosphere. The tantalum aggregate after the high-temperature heat treatment step is pulverized, and magnesium is added thereto. A low-temperature heat treatment step of performing low-temperature heat treatment under reduced pressure, and a method of producing tantalum powder having an acid washing step of washing the same with an acidic solution, wherein 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 tantalum powder in which the low-temperature heat treatment step is performed at a temperature of 700 ° C to 1000 ° C.

2. When reducing potassium tantalum fluoride with sodium, potassium tantalum fluoride and sodium are each divided into small portions in molten dilute salt, and the divided dilute salts are allowed to react with each other. 2. The tantalum powder according to claim 1, wherein the amount of the tantalum fluoride is always 40 to 1000 times the amount of the tantalum fluoride charged in the inside.

3. The method for producing tantalum powder according to claim 1, wherein the reduced tantalum powder has a specific surface area of 2 to 5 m2 g. .

4.Reduced tantalum powder having a specific surface area of 2 to 5 m ² / g, obtained by reducing tantalum fluoride power with sodium, is subjected to high-temperature heat treatment in an inert atmosphere, and then metal magnesium is added thereto. A tantalum powder obtained by performing a low-temperature heat treatment,

This tantalum powder is pressed to form a green body having a density of 4.5 to 5.0 g / cm ³ , and this green body is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature to obtain a green body having a density of the green body. A tantalum powder characterized by a sintered body having a density of 103 to 115% and a specific capacitance of 80,000 to 250,000 FV / g when this sintered body is formed at 60 ° (10 V).

5.Reduced tantalum powder having a specific surface area of 2 to 5 m ² / g, obtained by reducing potassium tantalum fluoride with sodium, is subjected to a high-temperature heat treatment under an inert atmosphere, and then a metal magnesium is added thereto, and then the mixture is treated under reduced pressure. A tantalum powder obtained by performing a low-temperature heat treatment,

Density from 4.5 to 5 The tantalum powder was press molded. And 0 g / cm ³ of the molded body, this When the green compact is vacuum-sintered at a temperature equal to or higher than the high-temperature heat treatment temperature to obtain a sintered body having a density of 103 to 115% of the density of the green body, the compressive strength of the sintered body after vacuum sintering is vacuum. 5. The tantalum powder according to claim 4, wherein the tantalum powder has 3 to 20 times the compressive strength of the compact before sintering.

6.Reduced tantalum powder with a specific surface area of ^{2 to 5} m ² Zg, obtained by reducing tantalum fluoride power with sodium, is subjected to high-temperature heat treatment in an inert atmosphere, followed by addition of metallic magnesium and low-temperature heat treatment under reduced pressure The tantalum powder obtained by performing

Density from 4.5 to 5 The tantalum powder by press molding. 0 and molding of GZcm ^3, and vacuum sintering the green body in this high-temperature heat treatment temperature or higher, 103 to the density of the green body A sintered body with a density of 115% was formed at 60 ° C and 10 V, and the specific capacitance was 80,000 to 250,000 uFV / g, and at 60 ° C, 20 V The specific capacitance of the product formed at 60 ° (: 70% or more of the specific capacitance of the product formed at 10 V powder.

7. A tantalum electrolytic capacitor obtained from the tantalum powder according to any one of claims 4 to 6.