JPH06267803A - Electrode material for capacitors - Google Patents

Abstract

(57) [Abstract] [Purpose] A capacitor having a small leakage current and a large capacitance is obtained by using a porous electrode composed of a dendritic intermetallic compound. [Structure] Dendritic intermetallic compound Al ₃ Zr
And a dendritic intermetallic compound obtained by forming any one of Al ₃ Hf and mixed powder thereof into a porous form by contacting with each other and sintering, and oxidizing the void surface of the porous body. The porous body is used as an electrode material of a capacitor. As a result, the capacitance of the capacitor can be about 2 to 40 times that of the conventional Al electrolytic capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material for capacitors, and more particularly to an intermetallic compound Al.
_{The present invention} relates to a porous electrode material for a capacitor, which is composed of a porous body obtained by molding and sintering a powder of ₃ Zr or Al ₃ Hf.

[0002]

2. Description of the Related Art Anode materials for conventional electrolytic capacitors include
A so-called valve metal is used which electrochemically produces a very thin oxide film and uses it as a dielectric. The most used metal among electrolytic capacitors is
Al is usually 99.99% or more in purity. The biggest problem of this aluminum electrolytic capacitor is to improve its capacitance. The method usually adopted for increasing the capacity is to increase the surface area by etching. However, at present, the surface area expansion rate has reached the limit, and further expansion is becoming difficult in terms of cost and quality control. Further, in the Ta capacitor, the surface area is expanded by sintering Ta powder, but Ta sintering requires a vacuum treatment at about 2000 ° C., and has a problem that it is very expensive in cost.

Electric double layer capacitors using carbon powder have been widely used for backup of semiconductor memories. This is obtained by utilizing the large surface area of the carbon powder of several m ² / g to number 100 m ² / g, the portion used as a capacitor is an electrolytic solution, the capacitor using an oxide of a conventional valve metal Since they are different from each other, the operating voltage is as low as 1 to 2 V, which makes it difficult to be applied to a general electronic component field.

A proposal is also made of a porous aluminum-titanium alloy sintered body using a composite metal for the purpose of both the Ta capacitor and the Al electrolytic capacitor (JP-A-60-147110). Has been done. However, in this case, the inventors of the present invention have found that the leakage current is large and cannot be improved even if some improvement is made.

As described above, the electrolytic capacitor has its capacity improved by improving etching, and the metal having a large dielectric constant such as Ta is used, but this is also the technical limit. . Further, although one using an aluminum-titanium based alloy porous sintered body has been proposed (JP-A-60-147110), the metal species is Al.
Since Ti is Ti and Ti, the leakage current is large and there is a drawback that it is not improved even with some improvement.

[0006]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems of the prior art, and to provide a new anode material for further increasing the capacity of the capacitor, which has reached the limit. Has an aim.

[0007]

The present inventors have found that Zr, H
A powder of an intermetallic compound having a particle size of 0.05 μm to 10 μm, which is formed of any one of f or two and f and Al,
Attention was paid to the use of a porous intermetallic compound for a capacitor, which is formed by being in contact with each other and sintered, and whose surface is oxidized, as an electrode material. As a result of various studies aimed at further increasing the capacity, the following findings were obtained to increase the capacity by making the powder form dendritic and giving a larger surface area. That is, any one of the intermetallic compounds Al ₃ Zr and Al ₃ Hf having a dendritic morphology, or a mixed powder thereof is contacted with each other and molded into a porous state and sintered, and It was clarified that a porous intermetallic compound obtained by oxidizing the surface of voids is used as an electrode material for capacitors.

The dendritic intermetallic compound used here is one of Zr and Hf in a total amount of less than 25 at%, or 2
In the rapidly solidified structure of the alloy consisting of the seed and the balance Al, A
This utilizes the fact that Al ₃ Zr and Al ₃ Hf crystallized in the l phase have a dendritic growth morphology. Al
These dendritic intermetallic compounds present in the phase are extracted by dissolving the Al phase with hydrochloric acid or the like. The size and dendritic spacing of the dendritic intermetallic compound can be changed by controlling the alloy component ratio and the cooling rate during solidification, and the size (a in FIG. 1 described later) is 0.5 to
Approximately 10 μm, tree spacing (b in FIG. 1 described later) is 0.01
A dendritic intermetallic compound of about 1 μm can be prepared.

The voids in the porous electrode formed and sintered using such a fine and complex dendritic intermetallic compound have a very large surface area. A large-capacity capacitor electrode material can be obtained by forming a dielectric oxide film for accumulating charges on the surface of the void having a large surface area. This is because it is possible to provide a larger surface area than that of a porous electrode produced using a commercially available intermetallic compound powder, and it is possible to further increase the capacity.

The present invention will be described in detail below. The dendritic intermetallic compound in the present invention includes Al ₃ Zr and Al.
_It is any one of ₃ Hf or a mixed powder thereof. As described above, as a method of giving the intermetallic compound a dendritic morphology, there is a method of utilizing a solidified structure.

For example, a method for producing a dendritic Al ₃ Zr powder will be described below. An alloy in which Al and Zr less than 25 at% are melted at a high temperature and rapidly solidified at a cooling rate of about 10 ² to 10 ⁴ ° C./sec is a dendritic Al ₃ Zr and Al.
It has a two-phase structure with. Of this alloy, only the Al phase is dissolved with dilute hydrochloric acid or the like, and only the dendritic Al ₃ Zr is extracted. This cooling rate can be realized by a method of casting the molten alloy in a copper mold in a thin plate shape, a method of injecting the molten alloy onto a single roll rotating at a high speed, or the like. The latter method, which provides a large cooling rate, is excellent for producing finer dendritic Al ₃ Zr, for example, with a dendritic spacing of 0.1 μm or less.

Next, the powder of the dendritic intermetallic compound is pressure-molded by a uniaxial press molding machine or the like. Then 10
Sinter at a temperature of 00 to 1300 ° C. for several hours. The sintering is performed in a vacuum of 10 ^-5 Torr or more. The porous electrode material obtained by pressure-molding and sintering the dendritic intermetallic compound is subjected to chemical conversion treatment to form an oxide film on the surface of the dendritic intermetallic compound. This oxide film, which is responsible for the accumulation of electric charges as a capacitor, has a large surface area because it is formed on the fine and complex shaped surface of the dendritic intermetallic compound. The voltage at this time is about 10 to 500 V, which is determined by the specifications of the capacitor used.
The chemical conversion liquid is the same as the chemical conversion liquid for a normal aluminum electrolytic capacitor.

On the other hand, the relative permittivity of the oxide film formed by the above method is 15 to 20, and the relative permittivity of the Al ₂ O ₃ oxide film in the aluminum electrolytic capacitor is 8.
It is large compared to 5-10. Further, in the manufacturing process of the aluminum electrolytic capacitor, in order to increase the surface area before chemical conversion, a step of etching the aluminum foil as the original foil is necessary, but in the present invention, the dendritic intermetallic compound powder is molded, Because it is used after sintering,
Of course, no etching is needed. However, etching may be performed to further increase the surface area of the molded product.

The porosity after molding is about 40% to 70%, but considering the characteristics of the capacitor, it is preferably about 55%. FIG. 1 is a schematic enlarged view of a porous electrode material obtained by pressure-forming and sintering a chemical conversion-treated dendritic intermetallic compound according to the present invention. The shaded area is a dendritic intermetallic compound.

As described above, the present invention provides a capacitor electrode material having a very large capacity by combining the large surface area of the dendritic intermetallic compound with the high dielectric constant of the oxide film formed thereon. To do.

[0016]

EXAMPLES The present invention will be further described below based on examples. 4 types of capacitors A, B,
Five prototypes of C and D were made, and then a characteristic evaluation test was conducted for each.

As the capacitor A intermetallic compound powder, dendritic Al ₃ Hf having an average size of 5 μm was used. The dendritic spacing of this dendritic Al ₃ Hf is about 0.2 μm. Dendritic Al ₃ Hf powder is 2
Hat of 0 at% and the remaining Al are melted and mixed at 1700 ° C., cast into a copper mold to prepare an alloy plate having a thickness of about 0.3 mm, and then the Al portion is melted in a 10% hydrochloric acid aqueous solution to manufacture. It was done. A coin-shaped molded body of 10 mmφ × 3 mmH was produced from this powder by a uniaxial molding press. The pressure during molding was 1.2 t / cm ² .
Next, this molded body was sintered in vacuum at 1200 ° C. for 1 hour. A lead was attached to this porous electrode, an insulating paste was applied to the unnecessary portion for chemical conversion, and then dried. Subsequently, a chemical conversion treatment was performed to electrochemically form an oxide film. The treatment voltage was DC 15V, and the treatment was performed in an ammonium phosphate solution. Next, after the cathode baking of MnO ₂ was performed by the manganese nitrate method that is often performed in Ta capacitors, graphite and silver paste baking were performed, and the cathode leads were drawn out to obtain capacitors.

As the intermetallic compound powder of the capacitor B , dendritic Al ₃ Hf having an average size of 3 μm was used. The dendritic spacing of this dendritic Al ₃ Hf is about 0.1 μm. Dendritic Al ₃ Hf powder is 1
Hat of 0 at% and the rest of Al were dissolved and mixed at 1700 ° C., and the mixture was poured onto a copper single roll rotating at a high speed to prepare an alloy flake having a thickness of about 0.1 mm. It is manufactured by dissolving. From this powder by a uniaxial molding press machine, 10mmφ × 3mm
A coin-shaped molded body of H was produced. The pressure during molding is 1.
It was set to 0 t / cm ² . Next, this molded body was sintered in vacuum at 1100 ° C. for 1 hour. After attaching the leads, a capacitor was manufactured by the same method as the capacitor A.

As the capacitor C dendritic intermetallic compound powder, Al ₃ Zr powder having an average size of about 10 μm and a dendritic spacing of about 0.3 μm was used. This dendritic Al ₃ Zr powder was prepared by dissolving and mixing 20 at% of Zr and the remaining Al at 1600 ° C., casting the mixture in a copper mold, and producing an alloy plate having a thickness of about 0.3 mm.
Manufactured by dissolving the Al portion in a hydrochloric acid aqueous solution. This powder is uniaxially pressed with a 10 mmφ
A coin-shaped molded body of × 3 mmH was formed. The pressure during molding was 1.5 t / cm ² . Next, this compact was sintered in vacuum at 1200 ° C. for 2 hours. Leads were attached to this, an insulating paste was applied to the unnecessary portions for chemical conversion, and then dried. Subsequently, a chemical conversion treatment was performed to form an oxide film. The treatment conditions were a voltage of 25 V and an ammonium phosphate solution. Then, MnO ₂ was subjected to cathodic baking by the manganese nitrate method which is often performed in a normal Ta capacitor. Next, after baking graphite and silver paste, a cathode lead was attached and resin molding was performed to obtain a capacitor.

[0020] As the capacitor D intermetallic compound powder, using a mixed powder of dendritic _Al 3 Hf and dendritic _Al 3 Zr average 5μm size. The dendritic spacing of this mixed dendritic powder is about 0.2 μm.
Mixed dendritic powder contains 10 at% Hf and 10 at%
Manufactured by dissolving and mixing Zr and the remaining Al at 1700 ° C., casting the mixture in a copper mold, making an alloy plate with a thickness of about 0.3 mm, and then dissolving the Al portion in a 10% hydrochloric acid aqueous solution. Is. A coin-shaped molded body of 10 mmφ × 3 mmH was produced from this mixed powder by a uniaxial molding press. The pressure during molding was 1.2 t / cm ² . Next, this molded body was sintered in vacuum at 1200 ° C. for 1 hour. After attaching the leads, a capacitor was manufactured by the same method as the capacitor A.

Table 1 shows the characteristic evaluation results of the capacitors A to D.

[Table 1] Capacitors A and B were produced by using dendritic Al ₃ Hf powders having different average sizes and intervals between branches. Compared to the capacitor A, the dendritic powder used in B has a small average size and a small dendritic spacing, so that the surface area of the prepared porous electrode is B, and the capacity is large. Also,
Capacitors A and D have almost the same average size and dendritic spacing, but capacitor A is Al ₃ Hf single powder, D
Is a mixed powder of Al ₃ Hf and Al ₃ Zr. In the oxide film formed on Al ₃ Hf and the oxide film on Al ₃ Zr, the latter has a smaller relative permittivity, and thus the capacity of D containing Al ₃ Zr powder is smaller.
The chemical conversion treatment voltage of the capacitor C is higher than that of the capacitors A, B, and D, and the surface area thereof is small because the oxide film formed is thick. As a result, the capacity is also reduced. However, it has an advantage that it is simpler than B as a method for producing powder. Regarding leakage current, capacitors A, B,
Both C and D have sufficient values as capacitors.

Comparative Example 1 A capacitor having a porous electrode made of a commercially available intermetallic compound powder as an anode was manufactured as a prototype. As the intermetallic compound powder, Al ₃ Hf having an average particle size of 0.3 μm was used. From this powder with a uniaxial molding press machine, 10 mmφ x 3 mmH
A coin-shaped molded body of was produced. The pressure during molding is 1.2
It was set to t / cm ² . Next, this molded body was sintered in vacuum at 1200 ° C. for 1 hour. A lead was attached to this porous electrode, an insulating paste was applied to the unnecessary portion for chemical conversion, and then dried. Next, chemical conversion treatment was performed to electrochemically form an oxide film. The treatment voltage was DC 15 V, and the treatment was performed in an ammonium phosphate solution. Next, after the cathode baking of MnO ₂ was performed by the manganese nitrate method that is often performed in Ta capacitors, graphite and silver paste baking were performed, and the cathode leads were drawn out to obtain capacitors. This is the same as the manufacturing method of the capacitor A in the example except for the form of the intermetallic compound powder.

Table 2 shows the evaluation results of the characteristics of the four prototype capacitors.

[Table 2] The capacity of the capacitor A (Table 1) exceeds the capacity of this comparative example (Table 2). This is because even if the same Al ₃ Hf powder was used, a porous electrode having a larger surface area could be produced by making the powder form dendritic.

[0024]

As described above, according to the present invention, the capacitance of the capacitor is 2 times that of the conventional Al electrolytic capacitor.
It has become possible to manufacture a large-capacity capacitor having a value of about 40 times.

[Brief description of drawings]

FIG. 1 is an enlarged view of a porous electrode material obtained by pressure-molding and sintering a dendritic intermetallic compound of the present invention.

Claims (1)

[Claims] 1. An intermetallic compound Al ₃ Z having a dendritic morphology.
Porous substance for a capacitor, which is formed by arranging any one of r and Al ₃ Hf, or a mixed powder thereof, into a porous form by contacting with each other, and by oxidizing the surface of voids of the porous body. Electrode material.