JP2006516039A - Method for producing niobium powder and / or tantalum powder having a large surface area - Google Patents

Abstract

The present invention is a method for producing niobium powder and / or tantalum powder having high purity, large specific surface area, controlled content of oxygen and nitrogen, and a form suitable for use in the production of capacitors. A controlled layer of niobium oxide and / or tantalum oxide (Nb _x O _y and / or Ta _x O _y , where x = 1 to 2 and y = 1 to 5), The layer carefully formed on the particles of metal niobium and / or metal tantalum and / or their hydrides of appropriate purity can be transformed into an alkali metal or alkaline earth metal and / or them in a molten salt bath. And a subsequent step of recovering niobium powder and / or tantalum powder by dissolving the salt in an aqueous solution. These particles produced using the method described above have a small particle size, a large surface area, and a sponge-like morphology, which makes them suitable for manufacturing capacitors.

Description

The present invention is a controlled layer of niobium oxide and / or tantalum oxide [Nb _x O _y and / or Ta _x O _y (where x = 1 to 2 and y = 1 to 5)]. And carefully formed on high purity metal niobium and / or metal tantalum and / or their hydride particles by a reaction metal dissolved in a molten salt solution in a controlled atmosphere. The present invention relates to a method for producing niobium powder and / or tantalum powder by reducing the layer.

U.S. Patent No. 1,728,941; U.S. Patent No. 2,516,863; U.S. Patent No. 4,687,632; U.S. Patent No. 6,136,062; U.S. Patent No. 6,171,363; Niobium and / or other refractory metal oxides, as described in German Patent No. 19833280; and International Publication No. 00/15555, by alkali metal or alkaline earth metal metals and / or hydrides. Reduction is well known.
The main problem of the metallothermal reaction is that it is a highly exothermic uncontrolled reaction where the equipment is overheated and the properties of the powder produced (increased average particle size, and This is a reaction in which the reduction of the specific surface area is impaired.

  One way to control the reaction is to initially reduce the niobium suboxide, as described in several patent specifications. This is because, under these conditions, the exothermic characteristics of the reaction are not so intense. The suboxide thus produced will then be reduced again to niobium metal by a less intense exothermic behavior to produce a powder with the recommended properties. However, such a procedure creates the need to perform the process in two stages and increases the consumption of energy and time. In addition, the powder is more likely to become contaminated due to the high temperature contact with the oven atmosphere; the reducing agent; and the vessel in which the reaction takes place in more stages. Some patent specifications utilize the need to use forced reactor cooling and / or mechanical agitation devices to reduce the exothermic effects of the reaction and to promote heat dissipation. The need to do is described. Another form of reaction that has been described involves the use of alkali metals or alkaline earth metals in vapor form. The use of steam is permitted to eliminate the problems that occur when the reducing agent is used in the liquid state. However, if this technique is used, it is often necessary to perform a subsequent deoxygenation step. This is because almost always a complete reduction cannot be achieved with only one step. Furthermore, although the evaporation of alkali metals or alkaline earth metals is endothermic, the reduction of niobium oxide using these metals in vapor form is more exothermic than if they are used in liquid form. This is disadvantageous for controlling the reaction in the direction of avoiding overheating.

  The use of reduction techniques in molten salt to produce niobium and / or other refractory metals has been described. However, other sources of niobium (eg, potassium fluoroniobate) are used; sodium is used as the reducing agent (US Pat. No. 4,684,399); or as a diluent While using a molten salt bath composed of KCl-KF or KCl-NaCl, the same compound is reduced with sodium (WO 01/59166); Reduced by the reactive metal dissolved in the solution (US Pat. No. 4,725,312 and WO 01/59166).

The method disclosed in US Pat. No. 4,725,312 and WO 01/59166 is a method for producing metals in group IV-B and VB powder form of the periodic table of elements. Then, a method for producing the metal by reducing a salt of the metal using a molten salt bath containing lithium as a reducing agent has been proposed. Various binary mixtures of salts have been described, among others LiCl-KCl, CsCl-LiCl, RbCl-LiBr, and KBr-LiBr, LiCl-NaCl-CsCl, LiCl-NaCl-RbCl, and LiCl-KCl-KF Seems to have been pointed out. In this method, the salt bath is maintained at a temperature of 400-550 ° C. The amount of lithium present in the molten salt bath is preferably at least the theoretical amount necessary to reduce Nb, Ti and Nd chlorides, and these chlorides are solid, liquid or gaseous. In some cases, the latter is preferred.
Patent application publications WO 01/82318 and 01/59166 use sodium as a reducing agent added to a bath of molten salt (KCl-KF or KCl-NaCl), and K ₂ NbF ₇ The production of niobium powder by reduction is described.

The main advantages of using the molten salt reduction method are: a) heat dissipation resulting from the reaction occurs in the salt bath, thus avoiding local overheating, and b) dissolving the reducing agent in the molten salt. The reduction potential of the reducing agent can be controlled, and c) by continuously supplying both the reducing agent and the raw material containing Nb and / or Ta to the salt bath to control the reduction rate. And, as a result, the generation of heat can be controlled, d) direct contact between the reducing agent and the source of Nb and / or Ta is avoided, and the Nb and / or thus obtained Reduced possibility of sintering and insufficient growth of Ta powder, e) it is possible to agitate the salt bath, and thus the reducing agent in the molten salt and the source of Nb and / or Ta To increase or decrease the dissolution rate of both F) the reaction temperature can be controlled by appropriately selecting the salt solution whose melting temperature matches the temperature at which it is desired to carry out the reaction. G) that in order to recover the Nb and / or Ta thus obtained, it is only necessary to dissolve the salt in an aqueous solution, so that the powder can be easily recovered, h) an alkali metal Or the alkaline earth metal oxide is dissolved in the salt, preventing the formation of a barrier between the reactant and the reducing agent, i) powdered or granulated form J) Injecting N ₂ gas into a salt bath or having a nitrogen as a doping element, which can be dissolved in molten salt Depending on whether the drug is used, The doping element can be introduced into Nb and / or Ta via the atmosphere of an oven that keeps it in a molten state, and k) an agent having phosphorus as a doping element that can be dissolved in the molten salt The doping element can be introduced into Nb and / or Ta using

  Using this method, niobium oxide and / or tantalum oxide can be reduced in a controlled manner using a powerful reducing agent that produces a high purity powder having a sponge-like morphology with a low apparent density and a high specific surface area. can do. In addition, the raw materials are high purity and appropriately sized metal niobium and / or metal tantalum and / or their hydrides that have been previously oxidized in a controlled manner to have the appropriate layer of oxide. Therefore, the thermal energy generated when the oxide layer is reduced is much smaller than the thermal energy generated in order to obtain the same particles when the raw material is made entirely of oxide. This smaller energy generation makes it easier to control the process in such a way that the possibility of contamination by gases and other metals is significantly reduced. The smaller energy generation can be demonstrated by the low leakage current of the powder obtained using the method.

  The present invention is a method for producing niobium and / or tantalum metal powders by performing a metal thermal reduction with a molten salt, the problem of overheating during the reduction; or a process with more than one step. The production method of solving the problem of need to be carried out is included.

  With such a method, due to the presence of a salt bath, the heat generated in the mixture is controlled and dissipated, and as a result, the feed rates of the reactants are controlled to directly reduce the reducing agent and the reactants. By avoiding contact, it is possible to control the reaction rate. In addition to the thermal aspect, the reaction is further controlled due to the possibility of controlling the potential of the reducing agent since the reducing agent is diluted to the salt in the desired concentration. In this way, the driving force for reduction can be controlled, and the control of the method can be enhanced. A high-purity raw material of suitable particle size in powder form, consisting essentially of metallic niobium and / or metallic tantalum and / or their hydrides, said raw material (hereinafter referred to as pre-oxidized in a controlled manner) "Oxidized powder") is a homogeneous precipitate of Nb and / or Ta having a sponge appearance in a liquid salt medium without forming clusters of undesirable dimensions The precipitate is created, creating an appropriate particle distribution.

The reducing agent is an alkali metal or alkaline earth metal, preferably calcium or magnesium and / or a hydride of such a metal. Alkali metal or alkaline earth metal nitrides can also be fed to a reactor consisting of an N ₂ source to obtain the niobium and / or tantalum produced.
The reaction takes place in an inert atmosphere (argon or helium); or in a reactive atmosphere containing, for example, nitrogen (N ₂ ); at a temperature between 300-1200 ° C., preferably between 500-1000 ° C.
While the reaction takes place, the salt is mechanically stirred, or an inert gas or a partially inert gas containing, for example, N ₂ is injected into the salt. The molten salt may be composed of a mixture of salts or a mixture of pure salts (eg, fluorides and chlorides of Ca, Li, Ba, Mg, K and Na). Salts that exhibit greater solubility of the reducing agent (eg, CaCl ₂ when using calcium as the reducing agent) are preferred.

The reducing agent and the oxidized Nb powder and / or Ta powder can be continuously supplied to the molten salt using an apparatus capable of controlling the supply rate of both. The temperature of the process can be kept constant by controlling the feed rate of the raw materials. The amount of the reducing agent used is desirably at least a stoichiometric amount for reducing all oxides of the supplied Nb and / or Ta oxide powder. An amount up to 800% of its stoichiometry can be used. Such excess depends on, among other parameters, the amount of salt bath.
Both the reducing agent and “oxidized powder” can be added to the reduction reactor together with the salt bath before the melting step, or are fed separately or together into the salt bath before the salt melts. be able to. This feeding step can be carried out continuously or otherwise. The amount of the reducing agent is substantially smaller than when the oxide particles are reduced, and depends on the oxygen content of the oxidized powder. Also, the required amount of reducing agent can be added to the salt bath in advance.

The following salts or mixtures thereof: CaCl ₂ , NaCl, KCl and MgCl ₂ can usually be used to control the reaction. With a mixture of these salts, reduction can occur at lower temperatures, and smaller particle sizes and larger surface areas can be obtained. The amount of salt or the amount of a mixture of salts affects the control of the reaction temperature, the higher the amount of salt, the easier it is to control the temperature. The amount of salt used may vary between 5 and 100 g per gram of oxidized powder supplied.
The reaction can be carried out in stainless steel, nickel, tantalum or niobium reactors, depending on the acceptable degree of contamination of the resulting product.

After the reaction, the resulting salt mixture containing the metal niobium and / or metal tantalum is dissolved in deionized water and then filtered, a solution containing HCl, HF, HNO ₃ and H ₂ SO Leaching with the solution which can also contain ₄ After leaching, the material is washed and dried.
The amount of water for solubilizing the salt varies between 10 and 100 liters for every 5 kg of salt. For the acid leaching step, 1-100 ml of solution is used for every 1 g of powder obtained by dissolution of the salt.

Control of the nitrogen content in Nb and / or Ta is achieved by controlling the N ₂ partial pressure in the oven atmosphere; N ₂ gas in the molten salt or a mixture of gases containing N ₂ Or else by adding a N ₂ carrier element (eg, a nitride that can be dissolved in the molten salt). A portion of nitrogen can be dissolved in a salt solution and nitride ions can be utilized to solubilize nitrogen in Nb and / or Ta particles. Similarly, phosphorus can be doped by adding a phosphorus compound that can be dissolved in a salt bath.

The Nb and / or Ta powder particles produced using this method have a reduced particle size, a large surface area and a sponge-like morphology, and are suitable for manufacturing capacitors. ing.
The reduction process initially involves melting the salt in a stainless steel, nickel, niobium or tantalum reactor in an inert gas atmosphere in the presence or absence of oxidizing powder and reducing agent. The oven chamber is preferably evacuated before heating the reactor and then pressurized with an inert gas at a pressure that can vary from 400 to 1200 Torr. After the salt melts, its temperature stabilizes at a temperature 30 to 150 ° C. higher than the melting point of the salt or the reducing metal, even if either the salt or the reducing metal has a higher melting point. Let From this point on, the bath agitation process is started by using a mechanical stirrer; or by injecting an inert or reactive gas (N ₂ or a mixture of N ₂ and inert gas). If the reducing agent and / or “oxidized powder” has not been previously added, begin adding both or one of them using a suitable device that can control the feed rate to the salt bath.

After the time required for the reaction has elapsed, the stirring is interrupted, the oven is turned off, and the salt containing metal Nb and / or metal Ta is cooled.
The time required for the reaction depends on the supply rate of the reducing agent or oxidized powder; or the amount of powder and reducing agent supplied together with the salt before the start of the reaction.
The feed rate of the oxidized powder is an important parameter for controlling the process. This is because local generation of heat can be controlled by the supply rate. However, as explained previously, this amount of heat is substantially smaller than when Nb oxide and / or Ta oxide is used as the source of Nb and / or Ta.

The reduction temperature can be affected by the surface area of the powder produced. High temperatures can result in larger particles having a smaller specific surface area. Therefore, selecting a mixture of salts is important for reducing the temperature of the process.
It is also important to stir the salt in order to disperse the oxidized powder in order to avoid local overheating and to avoid segregation of the oxidized powder in the bath.

FIG. 1 is a schematic view of a reactor used for carrying out reduction with molten salt, wherein the oxidized powder is continuously fed into a crucible containing molten salt. In the crucible containing the molten salt is placed another container that is submerged in the molten salt, which contains the liquid alkali metal or alkaline earth metal. Identifications relating to FIG. 1 are: 1 crucible containing liquid alkali metal or alkaline earth metal; 2 crucible containing molten salt; 3 stirring shaft; 4 molten salt; 5 inert gas or Reactive gas inlet; 6- "oxidized powder"; 7-container containing "oxidized powder"therein;8-thermocouple; 9-oven chamber; and 10-vacuum system outlet It is.
In this apparatus, mechanical agitation can be substituted with agitation caused by injection of inert or reactive gas.

After cooling the reactor in an inert atmosphere, the produced material dissolves in deionized water. The solution obtained by dissolution of the salt is filtered and then leached with a solution containing HCl, HNO ₃ , H ₂ SO ₄ and HF. The amount of leaching solution used is from 1 to 100 ml per gram of filtered product, preferably from 10 to 40 ml per gram. After this leaching, a final wash with deionized water, filtration, and vacuum drying is performed.
The Nb and / or Ta powder obtained by the present invention has an Mg and Ca content of less than 500 ppm, a potassium content of less than 50 ppm, and an oxygen content of 1000 to 4000 ppm / (m ² / g). The total amount of Fe, Cr and Ni is less than 300 ppm, and the specific surface area is between 1 and 30 m ² / g.

The invention is illustrated in more detail by the examples described below.
(Example 1)
The closed reactor depicted in FIG. 1, which is equipped with another vessel containing 124 g of metallic calcium in 4 kg of calcium chloride, in an argon atmosphere (800 torr), Heated to a temperature of 900 ° C. After homogenizing the mixture by mechanical stirring, 100 g of “oxidized powder” (average particle size 2.3 μm) was added in a continuous manner. The mixture was reduced and then cooled to ambient temperature.
The material was removed from the reactor and dissolved in deionized water. The solid phase was leached for 90 minutes with an aqueous solution containing HCl and HF. This mixture was then filtered and washed with 10 liters of deionized water. The cake obtained by filtration was then vacuum dried. Chemical analysis of the resulting powder demonstrated that the oxygen content was reduced from 18,000 ppm to 3,850 ppm.

(Example 2)
The closed reactor depicted in FIG. 1, which is equipped with another vessel containing 124 g of metallic calcium in 4 kg of calcium chloride, in an argon atmosphere (800 torr), Heated to a temperature of 900 ° C. After homogenizing the mixture by mechanical stirring, 100 g (average particle size 18.6 μm) of “oxidized powder” was added in a continuous manner. The mixture was reduced and then cooled to ambient temperature.
The material was removed from the reactor and dissolved in deionized water. The solid phase was leached for 90 minutes with an aqueous solution containing HCl and HF. This mixture was then filtered and washed with 10 liters of deionized water. The cake obtained by filtration was then vacuum dried. Chemical analysis of the resulting powder demonstrated that the oxygen content was reduced from 6,300 ppm to 785 ppm.

(Example 3)
The closed reactor depicted in FIG. 1, which is equipped with another vessel containing 124 g of metallic calcium in 4 kg of calcium chloride, in an argon atmosphere (800 Torr), Heated to a temperature of 900 ° C. After homogenizing this mixture by mechanical stirring, 100 g of “oxidized powder” (average particle size 1.1 μm) was added in a continuous manner. The mixture was reduced and then cooled to ambient temperature.
The material was removed from the reactor and dissolved in deionized water. The solid phase was leached for 90 minutes with an aqueous solution containing HCl and HF. This mixture was then filtered and washed with 10 liters of deionized water. The cake obtained by filtration was then vacuum dried. Chemical analysis of the resulting powder demonstrated that the oxygen content was reduced from 52,210 ppm to 10,500 ppm [corresponding to 4565 ppm / (m ² / g)].

(Example 4)
The closed reactor depicted in FIG. 1, comprising therein another vessel containing 40 g of metallic magnesium in a mixture of 3.2 kg of calcium chloride and 0.8 kg of potassium chloride. Was heated to 900 ° C. in an argon atmosphere (800 Torr). After homogenizing this mixture by mechanical stirring, 100 g of “oxidized powder” (average particle size 1.9 μm) was added in a continuous manner. The mixture was reduced and then cooled to ambient temperature.
The material was removed from the reactor and dissolved in deionized water. The solid phase was leached for 90 minutes with an aqueous solution containing HCl and HF. This mixture was then filtered and washed with 10 liters of deionized water. The cake obtained by filtration was then vacuum dried. Chemical analysis of the resulting powder demonstrated that the oxygen content was reduced from 39,620 ppm to 6,700 ppm [corresponding to 4,188 ppm / (m ² / g)].

(Example 5)
As shown in FIG. 2, oxidized powder (11 g) was placed on a metal screen attached to the support shaft 11 inside the crucible 1. Metal magnesium (25 g) was placed in a reducer container (Ca / Mg, NbH) further attached to the support shaft 2. Inside the crucible was placed a mixture of calcium chloride (240 g) and potassium chloride (60 g) along with the oxidized powder and the metal magnesium. The crucible was sealed by welding a lid thereon. The mixture was heated to a temperature of 900 ° C. for 2 hours. The mixture was reduced and then cooled to ambient temperature.
The material was removed from the crucible and dissolved in deionized water. The solid phase was leached for 90 minutes with an aqueous solution containing HCl and HF. This mixture was then filtered and washed with deionized water. The cake obtained by filtration was then vacuum dried. Chemical analysis of the resulting powder demonstrated that the oxygen content was reduced from 52,210 ppm to 5,850 ppm [corresponding to 3,250 ppm / (m ² / g)].

(Example 6)
As shown in FIG. 2, oxidized powder (11 g) was placed on a metal screen attached to the support shaft 11 inside the crucible 1. Metal calcium (25 g) was placed in a reduction vessel (Ca / Mg, NbH) further attached to the support shaft. Inside the crucible, calcium chloride (300 g) was placed together with the oxidized powder and the metallic calcium. The crucible was sealed by welding a lid thereon. The mixture was heated to a temperature of 900 ° C. for 2 hours. The mixture was reduced and then cooled to ambient temperature.
The material was removed from the crucible and dissolved in deionized water. The solid phase was leached for 90 minutes with an aqueous solution containing HCl and HF. This mixture was then filtered and washed with deionized water. The cake obtained by filtration was then vacuum dried. Chemical analysis of the resulting powder demonstrated that the oxygen content was reduced from 52,210 ppm to 5,520 ppm [corresponding to 3,070 ppm / (m ² / g)].

  The typical morphology of the powder produced using the methods disclosed herein can be seen in the backscattered electron image shown in FIG.

The invention will be described in more detail with reference to the accompanying drawings. In the drawings, like numerals refer to like structures throughout the various views.
It is the schematic of the reactor for reduce | restoring oxidation powder. It is a figure which draws the detail of the support shaft in a crucible inside. FIG. 6 illustrates a backscattered electron image of a typical form of a powder produced using the method disclosed herein.

Claims (10)

  In a method for producing niobium powder and / or tantalum powder having a large surface area, an oxidized powder (a powder having a suitable particle size consisting essentially of high-purity metal niobium and / or metal tantalum and / or hydrides thereof) A powder previously oxidized in a controlled manner) in a molten salt bath or in a molten salt solution with an alkali metal or alkaline earth metal and / or a metal hydride thereof, followed by The above process comprising the steps of leaching, filtering, washing and then drying the product thus obtained.   The reduction step includes calcium and magnesium as reactive elements, or another alkali metal or alkaline earth metal and / or metal hydride thereof, niobium oxide and / or tantalum oxide, or their The manufacturing method of Claim 1 containing the said metal and / or metal hydride which can reduce | restore an oxidation compound.   The manufacturing method according to claim 1, wherein the bath contains one kind of molten salt or a mixture of plural kinds of molten salts composed of an alkali metal or alkaline earth metal chloride or fluoride. The manufacturing method according to claim 3, wherein the chloride or fluoride of alkali metal or alkaline earth metal includes CaCl ₂ , NaCl, MgCl ₂ , KCl, and CaF ₂ .   The production method according to claim 1, wherein the reduction step includes a salt bath at a temperature between 300 ° C. and 1200 ° C.   The production method according to claim 1, wherein the reduction of the oxidized metal is carried out in a salt bath with mechanical stirring or stirring with an inert gas or reactive gas containing nitrogen.   The process according to claim 1, wherein the oxidized powder is fed to the salt bath containing the reducing agent in a continuous and controlled manner.   The production method according to claim 1, wherein the mixing of the oxidized powder and the reducing agent in the salt bath is performed before the melting step. The reduction in the molten salt is from 0.0005 atm (0.506625 mbar) to 1 atm (1013.25 mbar) so as to obtain niobium and / or tantalum powders with a nitrogen content varying from 100 ppm to 70,000 ppm. ) or the inside of a controlled atmosphere having a nitrogen partial pressure which may vary between, in the molten salt, containing N ₂ gas, or the (N ₂ 0.1 to 50%) and an inert gas The process according to claim 1, which is carried out by injecting a mixture of N ₂ and by adding a nitrogen compound to the salt bath.   The step of recovering the niobium powder and / or tantalum powder is performed by procedures that solubilize the salt in water and then leach the resulting solid product by using an acidic aqueous solution containing HCl and HF. The manufacturing method according to claim 1.

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