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Method of production of tantalum powder with low impurity level

a technology of tantalum powder and impurity level, applied in the field of powder metallurgy, can solve the problems of increasing leakage current, inability to manufacture anodes for electrolytic capacitors with high specific charge, and breakdown of capacitors, and achieve the effect of reducing potassium heptafluotantala

Inactive Publication Date: 2008-05-08
KEMET BLUE POWDER CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0011] Disclosed and claimed herein are methods for the production of a tantalum powder in a reactor vessel. In one embodiment, a method includes depositing a tantalum coating onto an internal surface of a reactor vessel and onto at least one auxiliary accessory thereof. The method further includes adding a quantity of potassium heptafluotantalate to the reactor vessel having the tantalum coating, and adding a quantity of a mixture of alkali metal halides into the reactor vessel. Finally, the method includes reducing the potassium heptafluotantalate using sodium in the reactor vessel.

Problems solved by technology

Mechanical and electrochemical methods result in tantalum powder with low surface area that makes impossible to manufacture anodes for electrolytic capacitors with high specific charge.
Metallic and non-metallic impurities lead to degradation of the dielectric oxide film on a surface of tantalum powder, increasing the leakage current or causing breakdown of the capacitor.
Contamination by nickel, iron, and chromium occurs in more complex ways including corrosion of the equipment in alkali halide melt, accompanied with transition of these metals into a bulk of the melt in the form of ions.
Use of tantalum as a material of a reaction vessel and lid results in considerable expenditures for tantalum powder production.
However, the impurity levels coming from a material of a reactor and oxygen remain significant due to the high solubility of alkali metal oxides in the melt used.
This method is unable even theoretically to produce tantalum or niobium metal coating onto nickel or nickel-containing surface.
In addition, the use of tantalum powder as an active ingredient raises considerably the cost of the process.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0036] 10 kg of potassium heptafluotantalate and 7.5 kg of sodium chloride were loaded into a reactor vessel manufactured of nickel. Then a reactor was placed into a container from stainless steel with a water-cooled cover and evacuated down to pressure 10−2 Torr, filled with argon, heated up to 800° C. and soaked at this temperature for 1 hour before melting of salts. After that, temperature in the container was reduced down to 700° C. and continuously stirred for 1.3 hours, after which 3.1 kg of the melted sodium was introduced into the reactor. During reaction of reduction of tantalum temperature of melt smoothly raised up to 820° C. After soaking at this temperature for 0.5 hours, a reactor was cooled down to room temperature. Then tantalum powder with crystallized salt mixture was removed from the reactor vessel, crushed and washed by water. Later on tantalum powder was processed consistently in 10% hydrochloric acid and 1% hydrofluoric acid, taken accordingly in quantity of 1....

example 2

[0038] 10 kg of potassium heptafluotantalate and 7.5 kg of sodium chloride were loaded into a reactor vessel manufactured of SS316 stainless steel. The reactor was then placed into a stainless steel container with a water-cooled cover and evacuated down to pressure 10−2 Torr, filled with argon, heated up to 800° C., and then soaked at this temperature for 1 hour before melting of the salts. After that, the temperature in the container was reduced down to 700° C. and, at continuous stirring of the melt for 1.3 hours, 3.1 kg of the melted sodium was introduced into a reactor. During reaction of the reduction of the tantalum powder, the temperature of the melt was smoothly raised up to 820° C. After soaking at this temperature for 0.5 hours, the reactor was cooled down to room temperature. Thereafter, the tantalum powder with crystallized salt mixture was removed from the reactor vessel, crushed and washed by water.

[0039] The tantalum powder was later processed in 10% hydrochloric aci...

example 3

[0041] 10 kg of potassium heptafluotantalate and 7.5 kg of sodium chloride were loaded into a reactor vessel manufactured of the nickel alloy Inconel 600. The reactor was then placed into a stainless steel container with a water-cooled cover and evacuated down to pressure 10−2 Torr. The reactor was filled with argon, heated up to 800° C. and soaked at this temperature for 1 hour before melting of the salts. After that, the temperature in the container was reduced down to 700° C. while the melt was continuously stirred for 1.3 hours, after which 3.1 kg of the melted sodium was introduced into the reactor. During reduction reaction, the temperature of the melt was smoothly raised up to 820° C. After soaking at this temperature for 0.5 hours, the reactor was cooled down to room temperature.

[0042] The tantalum powder with crystallized salt mixture was then removed from the reactor vessel, crushed and washed by water. The tantalum powder was then processed consistently in 10% hydrochlor...

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Abstract

The production of tantalum powder having a low impurity level is provided by a method in which potassium heptafluotantalate is added to a mixture of alkali metal halides in reactor vessel in which the internal surface and auxiliary input accessories of the reactor are covered with a tantalum coating. In one embodiment, the production of tantalum powder with low impurity level includes depositing a protective tantalum coating onto an internal surface of the reactor vessel and auxiliary accessories of a reactor by electrolysis of a mixture of alkali metals halides and potassium heptafluotantalate.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] The application claims the benefit of U.S. Provisional Application No. 60 / 855,697, filed Oct. 30, 2006.FIELD OF INVENTION [0002] The present invention relates in general to a field of powder metallurgy and, more particularly, to the production of a tantalum powder with low impurity levels. BACKGROUND OF INVENTION [0003] Tantalum powder is an excellent material for manufacturing of electrolytic capacitors. Tantalum powder can be produced by several methods, including mechanical methods, electrochemical reduction of tantalum compounds in molten salts and known metallothermic reduction process. Mechanical and electrochemical methods result in tantalum powder with low surface area that makes impossible to manufacture anodes for electrolytic capacitors with high specific charge. Methods of chemical reduction allow producing fine powder, which is characterized by high specific surface. Commonly, tantalum powder is commercially produced by redu...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B22F9/16
CPCB22F9/20B22F2999/00C22B5/02C22B5/04C22B34/24C25D3/66B22F9/04
Inventor CRAWLEY, JOHNPOLYAKOV, EUGENY
Owner KEMET BLUE POWDER CORP
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