JPS6129136B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a porous sintered body for an electrolytic capacitor. Conventionally, so-called valve metals such as tantalum, niobium, zirconium, vanadium, and hafnium have been known as anode body materials for electrolytic capacitors, and in the past many researchers have investigated the use of these metals alone or in alloys. We have investigated the basic characteristics of electrolytic capacitors and considered their practical application. However, in order to be practical as a capacitor, the leakage current of the oxide film unique to the anode material,
Electrical properties such as dielectric loss must reach a certain level, and the only electrolytic capacitors currently in practical use use tantalum or aluminum as the anode body. Capacitors using tantalum as anode material have excellent electrical properties such as leakage current and dielectric loss.
Each capacitor is unique in that it is stable and extremely reliable, compact and has a large capacity, and capacitors using aluminum as the anode material are inexpensive. However, the supply of tantalum has not been able to keep up with the increase in demand over the past few years, and due in part to resource shortages, material prices have skyrocketed and product prices have risen. Furthermore, the situation is such that it may become difficult to maintain production in the future. On the other hand, although aluminum is a cheap metal,
Because the melting point is low and the powder particle surface is easily covered with a strong gas-phase oxide film, it is difficult to sinter the powder to obtain a porous body with a large surface area, making it impossible to obtain a small and large-capacity product. There are drawbacks. Therefore, there has been a strong desire to develop electrolytic capacitors whose anodes are made of materials that have excellent electrical properties such as leakage current and dielectric loss, can be made smaller and larger in capacity, and can be inexpensively and stably supplied. . As a result of various studies, the present inventors have found that a porous sintered body for electrolytic capacitors that meets such demands can be obtained when an aluminum-titanium alloy is used as the material for the anode body, and has already proposed the same. Porous anode bodies for aluminum-titanium electrolytic capacitors have abundant raw materials aluminum and titanium resources.
Conventional tantalum electrolytic capacitors or aluminum This can solve the problems of electrolytic capacitors. When putting this aluminum-titanium alloy electrolytic capacitor with excellent capacitor characteristics into practical use, a problem arises as to what material should be used for the embedded lead wire of the anode. The following conditions are required for materials that can be used as embedded lead wires. (1) Be a metal that can be anodized (i.e.
Valve action metal). (2) The electrical properties of the anodic oxide film (leakage current, loss, etc.) are excellent. (3) During sintering, the bonding reaction with the sintered body proceeds sufficiently,
The mechanical and electrical bond after sintering must be sufficiently strong. (4) Melting point is equal to or higher than aluminum-titanium alloy. (5) It must have workability that allows it to be put to practical use as an embedded lead wire. Conventionally, it has been customary to use lead wires made of the same material as the anode metal for the embedded lead wires in anode bodies for electrolytic capacitors, and for tantalum electrolytic capacitors, tantalum wires are
Aluminum wire is used in aluminum electrolytic capacitors. These lead wires satisfy all of the conditions (1) to (5) for lead wires in combination with their respective anode bodies. Therefore, if this customary practice is followed, it is first considered to use an aluminum-titanium alloy wire as a lead wire even in an electrolytic capacitor using an aluminum-titanium alloy as an anode body. However, as a result of investigation, it was found that the aluminum-titanium alloy wire satisfies the above-mentioned lead wire conditions (1) to (4), but has a problem in point (5). That is, aluminum-titanium alloys are generally hard and brittle, and have poor workability, making it difficult to make thin wires. Moreover, even if alloy wires are made, they tend to break when bent and are difficult to wind up onto reels, making it difficult to mass-produce sintered bodies using these wires as embedded lead wires. As a next step, they considered using aluminum wire, tantalum wire, or titanium wire. First of all, aluminum wire is
The melting point is lower than the sintering temperature of the aluminum-titanium alloy and does not satisfy condition (4) for lead wires. On the other hand, although tantalum wire satisfies all conditions (1) to (5), it is somewhat weak in terms of mechanical and electrical bonding properties with the sintered body (condition (3)). In other words, the melting point of tantalum is aluminum-
Since it is considerably higher than the melting point of titanium alloy, the mechanical and electrical bond between the wire and the sintered body during sintering is not as good as with a wire made of the same material as the sintered body. Therefore, in porous sintered bodies of aluminum-titanium alloys, where the sintered body tends to expand on the side with a higher aluminum content and the lead wire embedded part loosens, depending on the composition, the wire and the sintered body tend to be loose. In order to strengthen the mechanical and electrical connectivity of the lead wire, it is necessary to take measures such as providing a bent part in the embedded part of the lead wire. Furthermore, electrolytic capacitors using an aluminum-titanium alloy as the anode body were originally invented with the idea of overcoming the predicament of tantalum electrolytic capacitors due to the soaring price of tantalum raw materials caused by resource shortages. Therefore, using tantalum wire, which is more expensive per weight than tantalum powder due to added processing costs, as a lead wire does not meet the original purpose and is not a good idea. Furthermore, titanium wire satisfies conditions (1) and (3) to (5) for lead wires, but there is a problem with condition (2). In other words, although electrolytic capacitors using titanium as the anode metal have been extensively researched and considered in the past, they have not yet been put into practical use.As is clear from the fact that titanium's chemical formation characteristics are In particular, the leakage current is large, and it is difficult to say that it is good.
Therefore, the titanium wire cannot be used as a lead wire as it is. An object of the present invention is to provide a method for manufacturing an anode body for an electrolytic capacitor that can solve the above-mentioned problems with lead wires regarding an electrolytic capacitor using an aluminum-titanium alloy as an anode body. According to the present invention, in the method for manufacturing an anode body for an electrolytic capacitor by sintering a press-molded body of mixed powder of aluminum and titanium with a lead wire planted thereon, the lead wire is a titanium wire, and the lead wire is a titanium wire. A method for producing a porous sintered body for an electrolytic capacitor is obtained, characterized in that sintering is performed in an aluminum vapor atmosphere. According to the manufacturing method of the present invention, as will be explained in detail later, by vapor phase diffusion of aluminum vapor,
A sintered body of aluminum-titanium alloy is obtained which has a lead wire having an aluminum-titanium alloy layer formed uniformly from the surface to a depth of about 10 μm. Here, since the lead wire portion has an aluminum-titanium alloy layer formed on its surface within a sufficiently small thickness range relative to the wire diameter, the ratio of the alloy layer area to the wire radial cross-sectional area is small. Therefore, not only is the chemical properties of the wire portion good, but the flexibility of the original titanium wire is still sufficiently maintained. Although titanium wire, which originally has a problem with chemical conversion properties, is used, by sintering the pressed body in aluminum vapor, an aluminum-titanium alloy layer is formed on the surface layer of the wire, and a titanium phase (aluminum) is formed in the center. (including some solid-dissolved titanium phase), it became possible to simultaneously improve the chemical formation characteristics of the wire portion and the brittleness of the aluminum-titanium alloy wire. Also, unlike the case of the tantalum wire described above, an alloying reaction proceeds between the lead wire and the sintered body, so that a sufficient mechanical and electrical bond can be obtained. Therefore, when making a press molded product, lead/
There is no need to create any bends in the wire embedding part, and normal embedding press molding in a straight state is sufficient. As described above, the present invention utilizes the characteristics of aluminum having a low melting point and high vapor pressure,
For electrolytic capacitors that have a lead wire that satisfies all of the requirements (1) to (5) for the lead wire described above, even if titanium wire is used that has poor chemical properties such as leakage current. Its usefulness is obvious in that a porous sintered body can be obtained. Furthermore, the present invention is extremely effective in the sense that titanium wires that are already commercially available can be used as they are. The present invention will be explained in more detail with reference to Examples below. Mix titanium and aluminum powder so that the aluminum content is 54 atomic%, embed a titanium wire with a diameter of 0.5 mm as a lead wire, and
Pressure molding was performed at a pressure of ton/cm ² to obtain a press molded sample. The amount of mixed powder used per press molded body was 30 mg. Make a 10cm x 10cm x 5cm container with a lid using a tantalum plate and use this as the firing container. The reason why a container with a lid is used is to increase the degree of filling of aluminum vapor near the sample (ie, the press-formed body using a titanium wire as a lead wire). 20 pieces of the above press molded body are placed in this firing container.
A sample group (SG-) was obtained by putting the pieces in one piece and sintering them at 1050° C. under a reduced pressure of 1×10 ⁻⁶ mmHg to obtain a sintered body of aluminum-titanium alloy. Next, put 200 press molded bodies into the firing container and
The sample group (SG-) was sintered at 1050°C under a reduced pressure of 10 ^-6 mmHg. Furthermore, in order to increase the amount of aluminum vapor generated in the firing container,
In addition to 200 sample press molded bodies, aluminum
100 press molded bodies of 75 atomic% titanium-aluminum mixed powder were added together as an accompaniment material, and
The sample group (SG-) was sintered at 1050°C under a reduced pressure of 10 ^-6 mmHg. The amount of mixed powder used per one press molded body for accompaniment material was also 30 mg. All 20 sintered bodies of SG-, SG- and SG-
Randomly select 20 sintered bodies from each
Anodizing was performed at 50V, and the capacitance, tan〓, and leakage current when 10V was applied were measured, and 20 samples were collected in each group.
The average values for each sample were calculated and shown in Table 1.

[Table] Next, XMA analysis was performed on the sintered bodies of SG-, SG-, and SG-, 3 to 4 mm above the root of the lead wire for each group of four samples, and the AlKα peak and TiKα peak The results of determining the intensity ratio are shown in Table 2. It is estimated that the aluminum vapor pressure in the container during firing was approximately 1×10 ^-5 and 1×10 ^-4 mmHg at maximum for SG- and SG-, respectively.

[Table] The surface conditions of the wire surface before and after alloying, corresponding to before and after sintering, are shown in the scanning electron micrographs of the SG- sample in Figure 1 (before alloying) and Figure 2 (after alloying). show. Both magnifications are 500x. Furthermore, for SG-, the lead wire portion was embedded in resin and the radial cross section was polished to a mirror finish, and the results of XMA surface analysis on aluminum are shown in FIG. The magnification is 150x. The density of bright spots indicates the aluminum content, and it can be seen that the density of bright spots is high on the surface of the wire, and the wire is uniformly alloyed over the circumference over a constant thickness. On the other hand, the center (inner) part has a low brightness density and is a titanium phase with a slight solid solution of aluminum. The diameter of the titanium wire used was 0.5 mm, and aluminum
The thickness of the titanium alloy layer is approximately 10 μm. Now, according to Table 1, SG- and SG- have good leakage current characteristics, but SG-
The leakage current value is one and a half orders of magnitude larger than that of SG-. Comparing this with the results in Table 2, we find that SG
While the wire surfaces of − and SG− are sufficiently alloyed by vapor phase diffusion of aluminum vapor,
It can be seen that in SG-, the aluminum-titanium strength ratio is small and the alloying is insufficient, which is the cause of the large leakage current. As seen in the case of SG- and SG-, the situation can be improved by increasing the number of press-formed samples stored in a firing container of a certain size or by using supporting materials. If a suitable aluminum vapor atmosphere above a certain level is created, the surface layer of the titanium wire will have the properties shown in Figures 2 and 3.
An aluminum-titanium alloy layer as shown in the figure is formed, and a lead wire with good chemical properties can be obtained. Finally, in order to examine the degree of mechanical bonding between the sintered body and the lead wire, 90 sintered bodies were randomly selected from among the remaining 180 sintered bodies, excluding the 20 sintered bodies for the SG− and SG− chemical samples. As a result of applying a load of 5 kg in the direction of separating the sintered body and the lead wire, not a single lead wire came off. In addition, in order to examine the flexibility of the lead wires, a test was conducted in which each of the remaining 90 lead wires was bent at right angles at the middle portion, but none of the lead wires were bent. In contrast, a similar bending test was conducted on an alloy wire made from an alloy with a composition of Ti-54 atomic% Al.
After doing it 100 times, they all broke. These tests have confirmed that according to the present invention, the mechanical and electrical bonding of the sintered body lead wire is sufficient, and that the embedded lead wire of the sintered body has sufficient flexibility. It became clear. As explained above, according to the method of manufacturing a porous sintered body for electrolytic capacitors of the present invention, titanium wires that originally have poor chemical properties such as leakage current are used, and as a result, the It is clear that a porous sintered body for an electrolytic capacitor having a lead wire that satisfies all the conditions has been obtained, and that it is highly useful. Furthermore, it is clear that the present invention is extremely effective in the sense that titanium wires that are already commercially available can be used as they are.

[Brief explanation of the drawing]

Figure 1 is an electron micrograph showing the surface condition of the titanium wire before sintering (before alloying), Figure 2 is an electron micrograph showing the surface condition of the wire after sintering (alloying), and Figure 3 The figure shows the radial cross section of the lead wire section of the SG-sintered body of aluminum.
This is a photo showing the XMA surface analysis profile.

Claims (1)

[Claims] 1. A method for manufacturing a porous sintered body for an electrolytic capacitor by sintering a press-molded body of mixed powder of aluminum and titanium with a lead wire planted therein, wherein the lead wire is a titanium wire and the sintering is performed. Porous sintering for an electrolytic capacitor, wherein the porous sintering is carried out in an aluminum vapor atmosphere under reduced pressure, and the vapor pressure of the aluminum vapor atmosphere is equal to or higher than the equilibrium aluminum vapor pressure of a titanium-20 atomic % aluminum alloy at the sintering temperature. How the body is manufactured.