Method for preparing tantalum or niobium powders used for manufacturing capacitors

Abstract

Disclosed relates to a method for preparing tantalum or niobium powders used for manufacturing capacitors in an electrolytic reducing reactor including an anode, a cathode and a molten salt, the method comprising: obtaining a tantalum or niobium oxide, expressed by Ta2O(5-y) or Nb2O(5-y) where y=2.5 to 4.5, from a tantalum pentoxide Ta2O5 or a niobium pentoxide Nb2O5 generated partially by an alkaline metal electrolytically reduced via a first electrolytic reducing reaction that reduces an alkaline metal oxide from a molten salt comprising at least one metal halogen compound, selected from the group consisting of alkaline metal and alkaline earth metal, and an alkaline metal oxide on the cathode; and preparing a tantalum or niobium powder by a first electrolytic reducing reaction that reduces at least one metal halogen compound selected from the group consisting of the alkaline metal oxide and the alkaline earth metal on the cathode and by a second reducing reaction with the tantalum or niobium oxide, represented by Ta2O(5-y) or Nb2O(5-y) where y=2.5 to 4.5.

Description

BACKGOUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to a method for preparing tantalum or niobium powders used for manufacturing capacitors and, more particularly, to a method for preparing tantalum or niobium powders in high purity for manufacturing capacitors of high capacity from tantalum pentoxides Ta2O5 or niobium pentoxides Nb2O5 via a molten salt electrolytic reduction method.[0003]2. Description of Related Art[0004]Conventional methods for preparing tantalum powders include a method of reducing Ta2O5 via carbon, a method of reducing Ta2O5 via calcium and magnesium, a method of reducing TaCl5 via hydrogen and a method of reducing K2TaF7 via a molten salt electrolysis or via sodium. According to the carbon reduction method, the amount of remaining oxygen is very large. In case of calcium and magnesium reduction method, it is difficult to control the reaction. Besides, in case of the hydrogen reduction method, it is difficult to control ...

AI Technical Summary

Benefits of technology

The present invention provides a method for preparing tantalum or niobium powders used for manufacturing capacitors by inducing local sinterings of tantalum or niobium powders via heat of combustion reaction in the adiabatic process generated during the indirect reducing reaction with alkaline earth metals. The method involves obtaining tantalum or niobium oxide from tantalum pentoxide or niobium pentoxide generated partially by an alkaline metal electrolytically reduced via a first electrolytic reducing reaction that reduces an alkaline metal oxide from a molten salt comprising at least one metal halogen compound, and preparing a tantalum or niobium powder by a second electrolytic reducing reaction with the tantalum or niobium oxide. The method also includes leaching and washing the tantalum or niobium powders obtained during the second reducing reaction in an inorganic acid to obtain mesh structures. The use of tantalum pentoxides or niobium pentoxides with low metal impurities and carbon content is desirable. The technical effects of the invention include decreasing the addition of alkaline earth metal halogen compounds and providing a more efficient method for preparing tantalum or niobium powders for manufacturing capacitors.

Problems solved by technology

According to the carbon reduction method, the amount of remaining oxygen is very large.

In case of calcium and magnesium reduction method, it is difficult to control the reaction.

Besides, in case of the hydrogen reduction method, it is difficult to control the grain sizes.

Furthermore, the method of reducing K2TaF7 via the molten salt electrolysis prepares the powders in the form of dendrite, which results in a limitation on use.

However, this method still has some drawbacks that the yield is decreased due to unreacted reactants generated by applying a large amount of diluent for decreasing the temperature of reaction so as to prepare tantalum powders for manufacturing capacitors of high capacity and it is known that it is impossible to prepare the powders of 100,000 CV or more.

The most serious problem in those methods is that they are accompanied with strong exothermic reactions during reductions.

According to these methods, it is possible to synthesize minute tantalum and niobium powders by preventing such rapid increase of the reaction temperature, however, they still have some drawbacks that it is difficult to solve the problem of carbon contamination; they require a large amount of reducing agent and acid when leaching; and the reactions are made in two stages, which deteriorates their productivities.

When using the above method, it is possible to prepare tantalum powders having a capacity of 100,000 CV or more, however, it has still drawbacks that it requires a large amount of diluent in order to reduce the reaction heat generated during the reaction between Mg and Ta2O5 reduced via Na; the residual oxygen content in tantalum and niobium after reaction is very high, about 1 to 3.7%; and the final powders are dispersed in the molten salt, which causes difficulties in collecting the final powders.

Since the applied voltage cannot be increased, the reaction of electrolytic reduction proceeds slowly, which decreases productivity.

Besides, since the method aims at converting the metals themselves, it is not suitable for preparing tantalum and niobium powders used for manufacturing capacitors.

For this sake, it is required that primary grains having appropriate mesh structures be formed via local sinterings between initial grains reduced in the stage of metal reduction, however, it is difficult to expect the local sinterings between the reduced metal powders, since the oxygen atoms in the metal oxide are ionized directly to separate in case of the conventional direct electrolytic reduction process.

Moreover, in case of the conventional indirect electrolytic reduction process using alkaline earth metals, it is impossible to form mesh grains since heat of reaction in the adiabatic process is not generated during the direct reducing reaction with heavy metal oxides.

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