JPS6155563B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Subject of the Invention) The present invention relates to a method for producing tantalum powder, and particularly to a method for producing tantalum powder that is fine, has a low oxygen content, and has excellent capacitor properties.

(Prior Art) In the production of tantalum electrolytic capacitors, it has conventionally been desired that the raw tantalum powder contains as few other impurities as possible. The reason for this is that the presence of impurities in the oxide film or in the boundary with the tantalum particle base material forms metallographic defects, leading to an increase in capacitor characteristics, particularly leakage current, or destruction.

However, recently, proposals have been made to improve capacitor characteristics by actively adding a third component.

For example, Japanese Patent Publication No. 57-34321 discloses a powder that can be used to produce an anode with particularly improved capacitance by incorporating phosphorus into tantalum powder, and as a specific example, a powder that has improved flow characteristics. There is.

Furthermore, Japanese Patent Application Laid-Open No. 71614/1983 proposes a method for producing tantalum powder for electronic materials containing boron or a boron compound.

Furthermore, in U.S. Pat. No. 3,825,802, N, Si,
Proposals have been made for film-like metallic tantalum particles doped with dopants selected from P, B.

The third component in the prior art described above is not an impurity that inevitably intervenes, but rather an essential component that is added in an actively controlled limited amount to improve the characteristics of the tantalum powder or the capacitor using it. It will be done.

However, there is no technology that proposes an effective means for cleaning or preventing an increase in oxygen content during processes such as water washing, pickling, and vacuum heat treatment in the process of manufacturing tantalum powder by sodium reduction of potassium tantalate fluoride. Although it brings about a great improvement in tantalum capacitor characteristics, it has not been possible to see it in the past.

(Object of the Invention) In addition to efficient pulverization, the object of the present invention is to produce a tantalum powder that has excellent cleaning properties and condenser properties, especially with a low oxygen content in the tantalum powder, which has not been noticed by the above-mentioned prior art. It is about providing law.

(Structure of the Invention) The present invention is a method for producing tantalum powder by adding a magnesium component when reducing potassium tantalate fluoride with sodium in the presence of an alkali halide diluent.

The basic reaction between potassium tantalate fluoride and sodium is expressed by the following formula: K ₂ TaF ₇ +5Na→2KF+5NaF+Ta In the actual process of the above reaction, a diluent is used to lower the reaction temperature and facilitate the reaction. Alkali halide is added. The most frequently used alkali halide is NaCl, but KF, KCl
etc. are also often used.

An important point is the fact that most of the properties of tantalum powder for use in electrolytic capacitors are determined in the reduction step.

In general, the manufacturing process for tantalum powder, as shown in Figure 1, involves reducing the raw material K ₂ TaF ₇ with Na, then crushing the product, washing with water, pickling, sieving, vacuum heat treatment, and preparing the crushed powder. .

The present invention provides the above-mentioned tantalum powder manufacturing process,
It is characterized in that a magnesium component is added during Na reduction of K ₂ TaK ₇ to produce tantalum powder.

The magnesium component intervenes in the Ta metal lattice in an interstitial or intrusive manner and gives a kind of lattice defect to the Ta lattice, promoting the refinement of the Ta powder.As a result, the characteristics of tantalum capacitors such as specific capacitance, leakage current, Contributes to improvements in various characteristics such as power loss and breakdown voltage.

A part of the magnesium component may exist in Ta as Mg alone, but it may combine with O ₂ , which should originally combine with Ta, and be removed from the slag, or it may remain in the Ta powder.
Since O ₂ is fixed, it has the effect of preventing an increase in O ₂ , which is undesirable for binding with Ta. That is, in the vacuum heat treatment (10 ^-4 to ^{10 -5} Torr, about 1200°C, about 30 minutes) in the above step, the effect of preventing high-temperature oxidation of easily oxidizable tantalum is extremely large.

Although the process is located before vacuum heat treatment, the deoxidizing effect of Mg is expressed in the pickling process of Ta powder. produced by addition of magnesium component by using acid detergent H ₂ SO ₄ or HCl
MgO has the advantage of being extremely easily dissolved and removed.

To add magnesium component to Ta
MgCl ₂ and MgSO ₄ are the most common.

Addition of metallic magnesium is difficult to use from safety points of view, such as the fact that the metal itself is not inexpensive, its high temperature oxidation is extremely high, and there is a risk of explosive combustion.

The present invention will be explained below with reference to Examples.

(Example 1) 100Kg _{of K2TaF7} , 50Kg of NaCl, and _0.2Kg of MgCl2
Kg was mixed and reduced with Na33Kg at 800°C, and the resulting powder was processed according to the steps shown in FIG. 1 to obtain Mg-containing Ta powder A. An aqueous H ₂ SO ₄ solution was used as the pickling solution, and the vacuum heat treatment conditions were 10 ^-5 Torr,
It was heated at 1200℃ for 30 minutes. The average particle size of the obtained powder A is 3 μm, the bulk density is 1.65 g/cm ³ , and the Mg content is
The content of impurity O ₂ was 1.800 ppm. In addition, it had the following electrical characteristic values.

Specific capacitance CV=12000μFV/g Leakage current LC≒3.0μA/g Power loss tanδ=20% (Example 2) K ₂ TaF ₇ 100Kg, NaCl 50Kg, MgSO ₄ 0.3Kg to 33Kg
The resulting powder was treated in the same manner as in Example 1 to obtain magnesium component-containing Ta powder B. This powder B has an average particle size of 3.5 μm, a bulk density of 1.55 g/cm ³ , Mg 25 ppm, and an impurity O ₂ content.
1600ppm, CV=11000μFV/g, LC=3.0μ
A/g, tan δ=15% was obtained.

(Comparative example) K ₂ TaF ₇ 100Kg, NaCl50Kg, Na33Kg, 800
The reduction reaction product at °C was treated in the same manner as in Example 1 to obtain Ta powder C. The average particle size of the powder C is 7.5 μm, bulk density 3.2 g/cm ³ , impurity O ₂ content 2500 ppm, CV=6400 μFV/g, LC=1.5 μ
A/g, tan δ=15% was obtained.

Looking at the above Examples 1 and 2 and Comparative Examples, in both Examples 1 and 2 in which the method of the present invention was applied, the impurity O ₂ content in the Ta powder was greater than that of the comparative Ta powder that did not contain magnesium. It is known that the deoxidizing effect of the present invention is significant. Moreover, it is known that the specific capacitance of the capacitor in the electrical characteristics of the present invention is high, and the superiority of the present invention has been fully demonstrated.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the manufacturing process of tantalum powder.

Claims (1)

[Claims] 1. A method for producing tantalum powder, which comprises adding a magnesium component when reducing potassium fluorotantalate with sodium in the presence of an alkali halide diluent.