JP2003147403A - Niobium powder for manufacture of capacitor, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide niobium powder having excellent characteristics and high reliability and suitable for capacitors and to provide its manufacturing method. SOLUTION: The niobium powder consists of, by mass, <=7,000 ppm oxygen, <=200 ppm of one or more kinds among alkali metals and alkaline-earth metals and the balance essentially niobium. In the manufacturing method, reduction is performed at 600 to 900 deg.C for a period of time equivalent to the time required for regulating oxygen content in the niobium powder to be manufactured to 1,000 to 7,000 ppm by mass in the final stage of a reduction step in a process for reducing niobium oxide using one or more kinds among alkali metals and alkaline-earth metals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a niobium powder suitable for manufacturing a capacitor having excellent characteristics and high reliability, and a manufacturing method thereof.

[0002]

2. Description of the Related Art The niobium powder used for manufacturing a capacitor is preferably a fine powder having a large specific surface area because the capacity can be increased. Further, the niobium powder for manufacturing the capacitor is
It is desirable that the content of oxygen as an impurity is low in order to improve the sinterability.

Further, in order to produce fine niobium powder, an alkali metal or alkaline earth metal is mixed with niobium oxide or niobium fluoride and heated to cause a reduction reaction, and then niobium powder is produced from the reaction product. Is known, but this method can produce a niobium powder having a low oxygen content. However, if the above metals are added in excess, these elements will remain in the niobium powder. The residual additive element is considered to be solid-dissolved in niobium metal, and the capacitor manufactured from the niobium powder manufactured by the above method had insufficient characteristics and low reliability. That is, when anodizing the surface of the niobium powder sintered body, there is a problem that the formation of the dielectric layer is adversely affected in terms of homogeneity and stability, and the leakage current becomes large when used as a capacitor. Was there.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide niobium powder suitable for manufacturing a capacitor having excellent characteristics and high reliability, and a manufacturing method thereof.
Specifically, by improving the sinterability by reducing the amount of oxygen, and by reducing the residue of alkali metal or alkaline earth metal used as a reducing agent in niobium, the characteristics of the niobium oxide film itself are improved, and the capacitor is improved. It is an object of the present invention to provide niobium powder for capacitors, which has small characteristics, especially leakage current, and a method for manufacturing the same.

[0005]

The niobium powder for producing a capacitor of the present invention contains oxygen of 7,000 mass ppm or less and one or more kinds of alkali metals and alkaline earth metals of 200 mass ppm or less, and the balance is substantially the same. It is niobium.

The method for producing niobium powder for producing capacitors according to the present invention is a method of reducing niobium oxide with at least one of an alkali metal and an alkaline earth metal, and at the end of the reduction step, 650 ° C. or more. The reduction reaction is maintained at a temperature of 900 ° C. or lower for a time corresponding to the oxygen content of the niobium powder to be produced is 7,000 mass ppm or less and 1000 mass ppm or more. As a result, the capacity of the electrolytic capacitor can be maintained, and the sinterability of the powder and the leakage current in the oxide dielectric layer can be suppressed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In order to solve the above problems, the present inventor investigated in detail the relationship between the oxygen content and the alkali metal or alkaline earth metal content in the niobium powder obtained by the above method. It was As a result, they found that there was a negative correlation between these contents. That is, in the niobium powder obtained by the above method, the content of alkali metal or alkaline earth metal is likely to increase when the content of oxygen decreases. A case where Mg is actually reduced in an alkaline earth metal will be described below as an example. That is, when the reduction is insufficient and the oxygen content is as high as 10,000 mass ppm or more, the Mg content is as low as 10 to 50 mass ppm.

However, when the oxygen content is about 5000 ppm, the Mg content is increased to about 200 mass ppm. This Mg was considered to be a solid solution in the niobium metal powder.

Based on this, the present invention has been made on the basis of the following thoughts. That is, the alkali metal or the alkaline earth metal does not remain outside the metal niobium as an oxide, but forms a solid solution in the generated metal niobium. Then, the alkali metal or alkaline earth metal thus solid-dissolved deteriorates the characteristics of the capacitor and thus the reliability.
That is, if too much alkali metal or alkaline earth metal is dissolved, it adversely affects the formation of the dielectric layer when anodizing the surface of the niobium powder sinter, resulting in a large leakage current when used as a capacitor. I thought I would do it.

The niobium powder is molded and sintered into a sintered body. Further, the sintered body is anodized to form an oxide dielectric coating.

The niobium powder for capacitor production reduced with an alkali metal or an alkaline earth metal has an oxygen content of 700.
When it exceeds 0 mass ppm, the sinterability of the niobium powder decreases. Insufficient sintering of niobium powder makes it difficult to form a homogeneous and stable oxide dielectric film during anodization.
Consequently, the reliability of the capacitor cannot be improved sufficiently. On the other hand, when the reduction is lower than 1000 mass ppm, the residual amount of alkali metal or alkaline earth metal increases, and the content of alkali metal or alkaline earth metal in the niobium powder for manufacturing capacitors exceeds 200 mass ppm. In this case, the capacitor characteristics of the oxide dielectric film formed during anodic oxidation deteriorate. That is, the leakage current increases.

The manufacturing method of the present invention is a method for manufacturing the above-mentioned niobium powder for manufacturing a capacitor. By holding the reduction reaction at a temperature of 900 ° C. or lower at the end of the reduction step, the content of alkali metal and alkaline earth metal in the niobium powder is suppressed to an appropriate amount. It can be suppressed in this way because the diffusion of alkali metals and alkaline earth metals into the niobium powder is suppressed and the solubility of the alkali metals and alkaline earth metals in the niobium powder is reduced. Conceivable. On the other hand, at a temperature of 650 ° C or lower, the reduction reaction does not proceed.

The oxygen content in the niobium powder tends to decrease as the holding temperature at the end of the reduction step increases and as the holding time increases. Therefore, the holding time corresponding to the oxygen content of the manufactured niobium powder of 7,000 mass ppm or less and 1000 mass ppm or more can be obtained. The holding time at the end of the reduction step is preferably 1 hour or more, more preferably 2 hours or more, but not preferably more than 8 hours.

[0014]

EXAMPLES Next, the present invention will be further described with reference to examples.

[Examples 1 to 4] 100 g of niobium oxide powder
And 48 g of magnesium metal pieces in a niobium container,
After the inside was evacuated, an argon atmosphere was created. 9 in an airtight electric furnace that can create a gas atmosphere with the niobium container
After heating and reducing at 50 ° C. for 1 hour, the temperature was maintained at the following temperature for the following time to complete the reduction step. That is, Example 1 was kept at 800 ° C. for 3 hours, Example 2 was kept at 820 ° C. for 3 hours, Example 3 was kept at 840 ° C. for 3 hours, and Example 4 was kept at 790 ° C. for 6 hours. Then, the niobium container was allowed to cool in an argon stream.

Next, the reaction product was taken out of the stainless steel container in an argon stream and put into a 11.5N hydrochloric acid solution. Then, the reaction product was pickled to remove the produced magnesium oxide. Further, it was washed with water, washed with ethanol and then vacuum dried to obtain niobium powder. The contents of oxygen, Mg, Ca, Na and the like and the specific surface area of this powder were measured.

0.5 g of this niobium powder was weighed, compacted, and vacuum sintered at 1300 ° C. for 1 hour to obtain a porous sintered body. About this sintered body, 10 in phosphoric acid aqueous solution
Chemical conversion treatment was performed at a voltage of V for 10 hours. Then 35
LCR meter (Agilent 42
63B type) was used to measure the CV value (a general index representing the characteristics of the electrolytic capacitor, which is the product of the capacitance C and the formation voltage V). In addition, a leak current was measured by applying a DC voltage of 15 V using an electrometer. The results obtained are shown in Table 1.
Are also shown.

In Example 1, when the powder was heated and reduced at 950 ° C. for 1 hour, the reduction was stopped and the oxygen content of the powder was analyzed. As a result, it was 13000 ppm. Also,
In Example 4, after holding at 790 ° C. for 6 hours, reduction was stopped and the amount of oxygen in the powder was analyzed.
It was 600 ppm.

Example 5 100 g of niobium oxide powder, 23 g of metallic calcium powder, and 34 g of metallic magnesium piece were placed in a niobium container, and the inside was evacuated to an argon atmosphere. Here, the metallic calcium powder and the metallic magnesium piece were put in separate small containers so that they could be reacted with the niobium oxide powder at different times. Then, first, the whole of the niobium container is heated to 1200 in an electric furnace.
The niobium oxide powder and the calcium metal powder were reacted with each other for 1 hour by heating to ° C. Next, this reaction product and metallic magnesium were reacted at 900 ° C. for 1 hour. In addition, 82
The reduction step was completed by holding at 0 ° C for 3 hours. afterwards,
The niobium container was allowed to cool in an argon stream.

Next, the reaction product was taken out of the stainless steel container in an argon stream and charged in a hydrochloric acid solution. Then, the same test as in Example 1 was performed. The results obtained are shown in Table 1.
Are also shown.

[0021]

[Table 1]

The niobium powders of Examples 1 to 5 all have an oxygen content of 7,000 mass ppm or less and an alkali metal or alkaline earth metal content of 200 ppm or less. The sintered bodies produced from these powders all have high CV values and small leakage currents. Although Examples 1 to 3 are examples in which only the holding temperature at the end of the reduction step is different from each other, according to these examples, the holding temperature at the end of the reduction step becomes higher (lower) and oxygen The content is decreasing (increasing), and the Mg content is increasing (decreasing).

[Comparative Examples 1 to 4] 100 g of niobium oxide powder
And 48 g of metal magnesium pieces were placed in a stainless steel container, and the inside was evacuated to form an argon atmosphere. The stainless container was heated in an electric furnace at 900 ° C. for 3 hours, and then maintained at the following temperature for the following time to complete the reduction process. That is, Comparative Example 1 was kept at 600 ° C. for 2 hours, Comparative Example 2 was kept at 820 ° C. for 0.5 hours, Comparative Example 3 was kept at 980 ° C. for 3 hours, and Comparative Example 4 was kept at 1020 ° C. for 3 hours. Then, the stainless steel container was allowed to cool in an argon stream.

Next, the reaction product was taken out from the stainless steel container in an argon stream and charged in a hydrochloric acid solution. Thereafter, the same test as in Example 1 was conducted. Table 2 shows the obtained results.
Are also shown.

[0025]

[Table 2]

The niobium powders of Comparative Examples 1 and 2 have a leakage current of 100 nA or more, which is significantly larger than that of the Examples. This is because the retention time, that is, the reduction was insufficient, so that the oxygen content was higher than 7,000 mass ppm although the content of the alkali metal and the alkaline earth metal was low.

The niobium powders of Comparative Examples 3 and 4 were CV.
The value is low and the leakage current is extremely high. This is because the holding temperature at the end of the reduction step was raised above 900 ° C. too much, so that the oxygen content was low, but the alkali metal and alkaline earth metal contents were higher than 200 ppm.

[Comparative Example 5] 100 g of niobium oxide powder and 48 g of magnesium metal pieces were placed in a niobium container, and the interior was evacuated to an argon atmosphere. After heating the entire niobium container in an electric furnace at 950 ° C. for 1 hour,
The reduction step was completed by holding at 90 ° C for 3 hours. Then, the stainless steel container was allowed to cool in an argon stream.

Then, the reaction product was taken out from the niobium container in an argon stream and charged into a hydrochloric acid solution, and thereafter niobium powder was obtained in the same manner as in Example 1. And
The oxygen content of this powder was measured. As a result, about 860
It was 0 mass ppm.

[Prior Art Example 1] 100 g of niobium oxide powder and 48 g of magnesium metal pieces were placed in a stainless steel container, the inside was evacuated, and an argon atmosphere was created. The stainless container was heated in an electric furnace at 950 ° C. for 3 hours.
Then, the stainless steel container was allowed to cool in an argon stream.

Next, the reaction product was taken out of the stainless steel container in an argon stream and put into a 11.5N hydrochloric acid solution. Then, the reaction product was pickled to remove the produced magnesium oxide. Further, it was washed with water, washed with ethanol and then vacuum dried to obtain niobium powder. The oxygen and magnesium contents of this powder were measured. as a result,
Oxygen was 5500 mass ppm and Mg was 240 mass ppm.

[0032]

According to the present invention, it is possible to provide a niobium powder suitable for manufacturing a capacitor having high characteristics and high reliability, and a manufacturing method thereof.

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Claims (2)

[Claims] 1. A niobium powder for producing a capacitor, which contains 7,000 mass ppm or less of oxygen and 200 mass ppm or less of one or more kinds of an alkali metal and an alkaline earth metal, and the balance is substantially niobium. 2. A method of reducing niobium oxide with at least one of an alkali metal and an alkaline earth metal, wherein the niobium powder produced at a temperature of 650 ° C. or higher and 900 ° C. or lower is used at the end of the reduction step. A method for producing niobium powder for producing a capacitor, which comprises holding the reduction reaction for a time corresponding to an oxygen content of 7,000 mass ppm or less and 1000 mass ppm or more.