JP2003013115A - Method for manufacturing niobium and/or tantalum powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a niobium and/or tantalum powder of fine grain sizes suitable for an electrode material for capacitor, by suppressing a heat value in reaction when reducing niobium and/or tantalum oxide with alkaline earth metals and/or rare-earth metals by a simple method without employing complicated processes. SOLUTION: In this method, the powder 5 of niobium and/or tantalum oxide and the reducing metals 3 of alkaline earths and/or rare earths are separately disposed in a reaction vessel 2, the alkaline earths and/or rare earths metal are heated at 1400 deg.C or lower to vaporize them it, and the vapor is brought into contact with the powder 5 of niobium and/or tantalum oxide. Magnesium is preferably used for the reducing metal 3 in particular, and the temperature range of 800-1400 deg.C is preferable for the above heating temperature for vaporization.

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 niobium and / or tantalum powder suitable as an electrode material for a capacitor, and particularly to an alkaline earth metal and / or
Alternatively, the present invention relates to a method for producing niobium and / or tantalum powder by reducing niobium and / or tantalum oxide with a rare earth metal.

[0002]

2. Description of the Related Art As a method for producing a tantalum powder or a niobium powder, a method for reducing a niobium and / or tantalum compound using an alkaline earth metal and / or a rare earth metal as a reducing metal is already known. For example, JP-A-52-150
Japanese Patent No. 362 describes a method of obtaining a tantalum powder by adding a fine atomizing agent such as ammonium fluoride to potassium fluorotantalate and reducing it with sodium metal.

However, in the conventional method using such a reduced metal, when the mixture of the compound to be reduced and the reduced metal is heated to a predetermined temperature, the amount of heat generated by the reduction reaction is large and the reaction rapidly progresses. And the mixture is 1000 ℃
There is a problem in that the temperature rises to a temperature far above the temperature and control becomes impossible in a short time. Further, since the metal powder produced by such a reduction reaction at a high temperature becomes coarse, it is not possible to obtain a fine powder used as an anode or the like for a capacitor.

As a method for solving this problem and producing niobium and / or tantalum powder suitable as an electrode material for capacitors, Japanese Unexamined Patent Publication No. 2000-197710 discloses a reduction reaction which is divided into two steps to generate a calorific value. A method of suppressing has been proposed. In this method, a small amount and a fixed amount of oxide powder are continuously fed into a molten alkaline earth metal or rare earth metal at 750 to 950 ° C to carry out a first-stage reduction to a lower oxide, which is then acidified. After washing, a second-stage reduction is performed to produce a metal powder.

However, in this two-step reduction method, a complicated supply device is required because the oxide powder is continuously supplied in small amounts and in fixed amounts, and the temperature control system of the reaction system is difficult because cooling is required. Further, in addition to dividing the reduction reaction into two stages, after the reduction in the first stage, the oxide of the produced reduced metal and the excess reduced metal are washed and removed with an acid, which is a very complicated process. was there.

[0006]

SUMMARY OF THE INVENTION In view of the above conventional circumstances, the present invention requires a complicated process when reducing an oxide of niobium and / or tantalum with an alkaline earth metal and / or a rare earth metal. An object of the present invention is to provide a method for producing a niobium and / or tantalum metal powder having a fine particle size suitable as an electrode material for a capacitor, etc. by suppressing the heat generation amount of a reduction reaction by a simple method without passing through And

[0007]

In order to achieve the above-mentioned object, the method for producing niobium and / or tantalum powder provided by the present invention comprises an oxide of niobium and / or tantalum and an alkaline earth metal as a reducing metal. And / or a rare earth metal are placed separately in a reaction vessel, and the alkaline earth metal and / or the rare earth metal is heated to a temperature of 1400 ° C. or lower to be evaporated, and the vapor thereof is converted to niobium and / or tantalum oxide. It is characterized in that they are brought into contact with each other.

Further, in the above-mentioned method for producing niobium and / or tantalum powder of the present invention, magnesium is used as the reducing metal and heated to 800 to 1400 ° C. to bring the vapor of magnesium into contact with the oxide of niobium and / or tantalum. Can be made.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, reduction of niobium and / or tantalum oxide with an alkaline earth metal or a rare earth metal has a large reaction heat per unit mole, and therefore, the conventional method of directly mixing and reacting the two Not only is the reaction rate uncontrollable, the system temperature rises rapidly, the reduced metal powder coarsens, and the system pressure rises, which is dangerous.
In the method described in Japanese Patent Laid-Open No. 2000-119710 described above, the amount of heat generation is suppressed by dividing the reduction reaction into two stages, but it is difficult to control the temperature and the process is extremely complicated. It was hard to say that such a method.

In the present invention, by bringing the reduced metal vapor into contact with niobium and / or tantalum oxide,
The reaction rate can be slowly advanced, and the amount of heat generation per unit time can be suppressed. That is, the niobium oxide or tantalum oxide or a mixture thereof and the reducing metal alkaline earth metal or rare earth metal are arranged separately from each other, and it is possible to prevent a rapid reduction reaction from occurring by direct contact between them. At the same time, the alkaline earth metal or the rare earth metal is supplied as vapor to the oxide to cause a gradual reduction reaction.

The niobium and / or tantalum oxide as the raw material is not particularly limited, but niobium pentoxide or tantalum pentoxide can be preferably used, and a mixture thereof may be used. As the reducing metal, an alkaline earth metal such as magnesium or calcium, or a rare earth metal such as yttrium, lanthanum, or cerium can be used, and a mixture of these can also be used, for example, a mixture of a cerium group rare earth element. A certain misch metal or the like can also be preferably used.

The rate of the reduction reaction by the method of the present invention is much slower than in the case where the reducing metal, alkaline earth metal or rare earth metal, and niobium and / or tantalum oxide are in direct contact. Moreover, the reduction rate is determined by the vapor pressure of the reduced metal, and the vapor pressure can be controlled by the heating temperature of the reduced metal. That is, by adjusting the heating temperature of the reduced metal, the rate of the reduction reaction can be easily and stably controlled, and the reduction reaction can be stably proceeded without causing sudden heat generation.

Generally, the vapor pressure of the reduced metal increases as the heating temperature increases, and when the temperature decreases, the vapor supply amount decreases and the vapor pressure decreases. Therefore, it is necessary to heat to a temperature above the melting point of the reducing metal to be used and at which evaporation is possible, but if the heating temperature is too low, the time until the end of the reduction becomes long. On the other hand, if the heating temperature is too high, the vapor pressure becomes high and the reaction proceeds rapidly, so that the heat of reaction per unit time also becomes large, and further the pressure in the system rises rapidly, which is dangerous.

The heating temperature of the reducing metal may be appropriately determined according to the alkaline earth metal or rare earth metal used as the reducing metal so that an appropriate vapor pressure can be obtained. Especially, when the reducing metal is magnesium, the melting temperature is about 65.
Although it is 0 ° C, it is preferable to set the heating temperature to 800 ° C or higher. This is because if the heating temperature is lower than 800 ° C., the evaporation of magnesium does not proceed sufficiently due to the endothermic heat accompanying volatilization.

Further, since the niobium and / or tantalum powder obtained by the reduction is sintered and becomes coarse at a temperature exceeding 1400 ° C., the temperature near at least the oxide of niobium and / or tantalum needs to be 1400 ° C. or lower. Therefore, the heating temperature of the reduced metal is also set to 1400 ° C. or lower. It should be noted that, while the reduced metal and its surroundings generate heat absorption due to volatilization as described above, while the niobium and / or tantalum oxide and its surroundings generate heat due to the reduction reaction, the apparatus becomes complicated, but the reaction vessel It is desirable to control the temperature of each part independently.

The reduction of niobium and / or tantalum oxide is preferably carried out in an inert gas atmosphere in order to promote a uniform and stable reduction reaction. As the inert gas, nitrogen or argon can be used. Further, the amount of the alkaline earth metal or the rare earth metal which is a reducing metal is stoichiometrically required to be 1 molar equivalent of niobium and / or tantalum oxide, but preferably 1.3 molar equivalents or more.

In this way, the reduced metal vapor can be uniformly diffused in the reaction vessel, and the reduced metal vapor can cause the reduction reaction of niobium and / or tantalum oxide to proceed gently and uniformly. As a result, the niobium and / or tantalum oxide can be completely reduced to metallic niobium or metallic tantalum or its alloy in one reaction, and the obtained niobium and / or tantalum powder has a particle size of 1 μm.
The details are as follows. Moreover, it is only necessary to control the heating temperature of the reduced metal, and no complicated process or special device is required.

[0018]

EXAMPLE A cylindrical niobium reaction vessel 2 was placed in a vertical tubular electric furnace 1 shown in FIG. 1, and a niobium bucket 4 containing a reducing metal 3 was placed at the bottom of this reaction vessel 2 and above it. A niobium tray 6 containing niobium pentoxide powder or oxide powder 5 of tantalum pentoxide powder was placed and stored so as not to come into contact with the reduced metal 3. The oxide powder 5 had a thickness of about 3 cm (weight: 500 g), and the reduced metal 3 was 1.4 molar equivalents with respect to the oxide powder 5.

The niobium reaction vessel 2 is covered with a lid 2a, and the lid 2a
Argon gas was introduced into the interior from the gas supply port provided in the chamber to create an argon gas atmosphere. Next, the heating element 1 of the electric furnace 1
The inside of the reaction vessel 2 is heated to the temperature shown in Table 1 below by a.
Hold at that temperature for 4 hours. After cooling, the powder in the tray 6 made of niobium was taken out, dipped in 1N hydrochloric acid to remove the oxide of the reduced metal produced, and further washed with water and dried.

The BET specific surface area of each powder of Samples 1 to 8 thus obtained was measured, and
The oxygen content was analyzed and the results are also shown in Table 1 below. In this example, the oxide powder 5 was used because of the structure of the furnace.
And the reduced metal 3 are arranged separately in the vertical direction, but since the steam uniformly fills the inside of the container, the positional relationship between the oxide powder and the reduced metal is not particularly limited as long as they are separated from each other. You may arrange | position separately.

As a comparative example, in Sample 9, niobium pentoxide powder was used as the oxide powder and magnesium powder was used as the reduced metal, and both were directly mixed and placed in the niobium reaction vessel 2 and heated. The temperature was kept at 800 ° C. However, the temperature suddenly started to rise in the middle of heating and the temperature in the reaction vessel 2 exceeded 1400 ° C. and continued to rise, so it was judged dangerous and the test was stopped.

[0022]

[Table 1]

As can be seen from the above results, the reduced metal 3
In Samples 1 and 2 of the present invention using magnesium as
O content is as low as 0.8-0.9% by weight, and BET value is 9-.
Large as 11 m ² / g, extremely fine (average particle size 0.1-0.1
0.3 μm) metallic niobium powder and metallic tantalum powder. Further, in the case of the sample 3 of the present invention using calcium as the reducing metal and the sample 4 of the present invention using misch metal, a heating temperature higher than that of magnesium is required, but the O content is 0.9. Weight% and BET value are 7-
It is 8 m ² / g, and as with Samples 1 and 2, extremely fine metal niobium powder (average particle size 0.5 to 1 μm) is obtained.

On the other hand, in the comparative sample 5 which was carried out in the same manner as the sample 1 except that magnesium was used as the reducing metal 3 and the heating temperature was 750 ° C., the O content of the obtained powder was 3. It is as high as 5% by weight, and it can be seen that the reduction has hardly progressed because the temperature is too low. Also, in the sample 6 of the comparative example which was carried out in the same manner as the sample 3 except that calcium was used and the heating temperature was 800 ° C., the O content was 4.
It is as high as 2% by weight, and the reduction has hardly progressed.

On the other hand, the heating temperature of calcium is 1430 ° C.
In the sample 7 of the comparative example which was carried out in the same manner as the sample 3 except that the BET value of the powder was remarkably lowered to 0.3, although the O content was low and the reduction was sufficiently advanced. It can be seen that coarsening is occurring. In addition, in the sample 8 of the comparative example which was carried out in the same manner as the sample 1 except that the heating temperature of magnesium was set to 1450 ° C., the internal pressure suddenly increased during the temperature rise, magnesium vapor leaked out, and it was judged to be dangerous and tested. Canceled.

In Sample 8 and Sample 9 which were both judged to be dangerous and the test was stopped, the recovered powder contained the reduced metal powder, but in both cases, the average particle size was coarsened to 10 μm or more. It was Further, in this example, the temperature inside the oxide powder 5 was measured during the reaction, but in each of the samples 1 to 4 of the present invention and the samples 5 to 7 of the comparative example, abnormal heat generation due to the reduction reaction was observed. Was not done.

[0027]

According to the present invention, by supplying alkaline earth metal and / or rare earth metal as vapor to reduce niobium and / or tantalum oxide, the heating temperature can be reduced without complicated steps. It is possible to suppress the heat generation amount of the reduction reaction by controlling the above, and it is possible to manufacture a niobium and / or tantalum metal powder having a fine particle size suitable as an electrode material for capacitors and the like.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a specific example of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

1 electric furnace 1a heating element 2 Niobium reaction vessel 3 Reduced metal 4 niobium bucket 5 oxide powder 6 Niobium tray

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Claims (2)

[Claims] 1. A method for producing a niobium and / or tantalum metal powder by reducing an oxide of niobium and / or tantalum, which comprises an oxide of niobium and / or tantalum and an alkaline earth metal as a reducing metal. The metal and / or the rare earth metal are placed separately in a reaction vessel, the alkaline earth metal and / or the rare earth metal is heated to a temperature of 1400 ° C. or less to be evaporated, and the vapor is oxidized to niobium and / or tantalum. A method for producing niobium and / or tantalum powder, which comprises contacting an object. 2. The niobium and the niobium according to claim 1, wherein magnesium is used as the reducing metal and heated to 800 to 1400 ° C. to bring magnesium vapor into contact with niobium and / or tantalum oxide. / Or a method for producing tantalum powder.