JPH0413411B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum alloy electrode used in an electrolytic capacitor. The electrode material used in electrolytic capacitors is so-called valve metal, in which a very thin dielectric oxide film is electrochemically produced. Aluminum and tantalum are currently widely used as electrode materials. Of these, the dielectric material of the aluminum electrode is
The dielectric constant of Al ₂ O ₃ is approximately 7 to 10, which is by no means larger than the dielectric constant of other valve metals. For example, Ta ₂ O ₅ has a dielectric constant ε=25.2,
The dielectric constant ε of TiO ₂ is 66.1. For this reason, the aluminum foil used in aluminum electrolytic capacitors is etched at a considerably high rate to increase the surface area in order to increase the capacitance. In this etching process, an electrochemical or chemical etching method is being investigated in order to obtain a shape that geometrically maximizes the surface area, that is, an ideal etching form, taking into account the thickness of the foil. However, etching technology has progressed considerably, and at present it is no longer possible to double or triple the current surface magnification rate simply by making the surface finer. Furthermore, even if miniaturization is achieved, if a high anodic oxidation voltage is used, the etched shape cannot be fully utilized due to the so-called clogging phenomenon of the etched holes, resulting in a decrease in capacitance. Furthermore, when creating electrolytic capacitors, the interfacial contact with the electrolyte decreases,
This leads to a reduction in various properties such as an increase in foil resistance, an increase in tanδ, and a decrease in impedance characteristics. On the other hand, attempts have also been made to increase the capacitance using an anodizing method (chemical conversion method). This is a composite film of a boehmite film and an electrochemically generated film by pure water boiling treatment, a composite film of a chemical conversion film using a boric acid solution and a chemical conversion film using a phosphoric acid solution, and a special thin film is created in the pre-chemical treatment. Various studies are being conducted, including composite coatings with electrochemical coatings. However, no method has been found to significantly increase capacitance. As described above, it is extremely difficult to significantly increase capacitance by simply improving the etching treatment and chemical conversion treatment using the currently used 99.99% or 99.9% high purity aluminum. Even if the capacitance is increased by force, the leakage current increases and the withstand voltage decreases, which is not good. The present invention was developed based on this background with the aim of increasing capacitance without difficulty. The gist of the present invention is to change the dielectric material of an aluminum electrolytic capacitor from Al ₂ O ₃ alone to Al ₂ O ₃ +TiO ₂ and Al ₂ O ₃ +
Like ZrO ₂ , Al ₂ O ₃ + Nb ₂ O ₅ , Al ₂ O ₅ + HfO ₂
The purpose is to form a composite film with an oxide having a dielectric constant greater than that of Al ₂ O ₃ , thereby significantly increasing capacitance. The dielectric constant of Al ₂ O ₃ is 7-10, while that of TiO ₂ is 66.1 and that of ZrO _2.
31, Nb ₂ O ₅ is 47.1, HfO ₂ is 41.1, and these and
It can be easily assumed that the composite capacitance with Al ₂ O ₃ changes greatly depending on the mixing ratio. In recent patents, as seen in Japanese Patent Publication No. 58-15933, there is an example of sputtering aluminum and tantalum, alloying them on a substrate, and anodizing them to increase the dielectric constant of the dielectric film. I have not yet obtained anything that is fully satisfactory. The present invention was developed by liquid quenching an alloy of aluminum and a metal with a high dielectric constant such as titanium, zirconium, niobium, or hafnium, against the background that the technology for creating forced solid solution alloys has improved significantly in recent years. The purpose of this project is to create a uniformly dispersed aluminum alloy by forcing it into a solid solution using a method, and then use this as an electrode and perform anodic oxidation treatment to obtain high capacitance. In creating this forced solid solution alloy, the most important issue is the relationship between the rate of crystal nucleation and the rate of crystal growth during solidification of the supercooled liquid, and this has been carefully considered. In the case of alloys with aluminum, if the quenching time is long, for example in the case of aluminum-titanium, _three AlTi phases will be formed, and if the temperature falls below the peritectic temperature, the aluminum will solidify into a dendritic shape and grow into a petal shape. Put it away. Therefore, the quenching rate is
The temperature had to be at least 10 ⁶ °C/sec. The same thing was found for zirconium, niobium, and hafnium. Hereinafter, specific examples of the present invention will be described. It was created by melting 99.999% aluminum ingot and 99.9% titanium metal in an electron beam melting furnace in vacuum to form a mother alloy of 30% aluminum and 70% titanium in atomic percent. Pure aluminum was added to this to create aluminum master alloys with various titanium concentrations. The melting conditions at this time were to maintain the temperature 150°C higher than the liquidus temperature of each alloy for 40 minutes before casting into a mold. Furthermore, each ingot was homogenized and heated at 650℃ for 10 hours, then a small amount was cut out, remelted in a small high-frequency furnace, and rapidly cooled at a rate of ¹⁰⁶ ℃/second using a single roll method to form an aluminum plate with a width of 1cm and a thickness of 30μm. A titanium alloy foil was created. Observations using X-ray diffraction and transmission electron microscopy of these prepared samples revealed that they had a fine grain structure with a diameter of about 1 μm, and
Measurements using a wire microanalyzer also showed that titanium in the aluminum was completely uniformly dispersed. The sample prepared by the above method was treated with 6% hydrochloric acid.
Approx. AC etching treatment in 0.02% sulfuric acid solution
The surface area was increased by 10 times. Then, after thorough washing, the PH
= 6.5, a chemical conversion film up to 100 V was formed in an ammonia phosphate solution with a specific resistance of 200 Ωcm at 70°C. The capacitance of the sample coated with a chemical conversion film was measured using a capacitance bridge in a 5% ammonium borate solution.
℃, a constant current of 0.02 mA/cm ² was applied, a voltage increase curve was taken, and the bending point was taken as the withstand voltage. Table 1 shows the composition list of various aluminum-titanium forced solid solution alloys and the results regarding capacitance, breakdown voltage, and CV product.

[Table] As shown in Table 1, the CV product (capacitance x breakdown voltage) of the product of the present invention is significantly increased. As the titanium content increases, the CV product increases accordingly,
When the amount of titanium exceeds 60% in atomic percent, the voltage resistance of aluminum begins to decrease, resulting in
The CV product is decreasing. In addition, when the amount of titanium is 1%, there is almost no change observed compared to the one without additives. Therefore, it can be said that a titanium content of 2 to 60% is good. Similar experiments were conducted on zirconium, niobium, and hafnium, but similar to titanium, the CV
An increase in the product was observed. Moreover, the breakdown voltage at this time also decreased when the aluminum content was less than 40 atomic percent. Further, when the content was around 1%, no difference in CV product was observed, but it was observed when the content was 2% or more. Therefore, it can be said that a good content of zirconium, niobium, and hafnium is 2 to 60%. Furthermore, alloys containing two or more of these metals could be created in the same manner depending on the purpose. As described above, the CV product was significantly increased by the aluminum alloy electrode of the present invention, but even when it is commercialized, tan δ, L, C
was good, and the high frequency impedance was also excellent. One of the reasons why the impedance characteristics were good is that the aluminum alloy electrode foil of the present invention has fine grains and the alloy composition is forced into solid solution. Table 2 shows that an electrolytic capacitor with a rating of 80WV and 1000μF was manufactured using the aluminum alloy electrode foil described above, and a conventional product with the same rating was left continuously at 105℃.
The results of measuring and comparing leakage current every 250, 500, 750, and 1000 hours are shown. As is clear from Table 2, even in a no-load test at 105°C for 1000 hours, the leakage current increased by only about 1/5 compared to the conventional product. Needless to say, this is due to the fact that the dielectric film formed on the electrode is also dense and uniform.

[Table] As described above, when the aluminum alloy electrode for an electrolytic capacitor of the present invention is used, the characteristics as a capacitor are greatly improved, and a light, thin, short and small capacitor can be easily realized, and it has great industrial and practical value.

Claims (1)

[Claims] 1 An aluminum alloy containing 2 to 60 atomic percent of at least one of titanium, zirconium, niobium, and hafnium and unavoidable impurities is heated and melted, and the molten state is rapidly cooled to obtain a solid phase material. An aluminum alloy electrode for electrolytic capacitors manufactured by a liquid quenching method.