DE1113988B - Electrolytic capacitor - Google Patents

Description

INTERNAT. KL. HOIg

GERMAN

PATENT OFFICE

115590 Vmc / 21g

REGISTRATION DATE: OCTOBER 31, 1958

NOTICE
THE REGISTRATION
AND ISSUE OF
EDITORIAL: SEPTEMBER 21, 1961

The invention relates to electrolytic capacitors in which there is between the electrodes a solid, electrically semiconducting material is located and a dielectric layer between at least an electrode and the semiconducting material is arranged.

Capacitors of this type are referred to as "solid electrolyte capacitors" for Difference from the capacitors, which have a liquid electrolyte as a conductive material.

These capacitors, which contain a porous electrode made of valve metal, on their surface a dielectric film on which a semiconducting film was formed was produced by a forming treatment Oxide, which in turn is covered by a metal layer as a second electrode, are known. as The material used for the semiconducting oxide is manganese dioxide.

The function of the conductive oxide that is in contact with the dielectric film is to to supply oxygen to the latter so that the dielectric layer retains its insulating properties and is not interrupted anywhere. It can therefore replace the liquid electrolyte, which With the usual "wet" electrolytic capacitors, oxygen is added to the layer as a result of electrolytic processes.

Manganese dioxide, on the other hand, has the disadvantage that its electrical conductivity is only moderate. The capacitors made with it therefore still have a relatively large loss factor, which comes from the heat losses, especially at higher frequencies. Better conductive oxides can be used, but these have the disadvantage that they give off oxygen only with difficulty, so that their self-healing properties are only slight.

According to the invention it is possible to have good conductivity with good self-healing properties to connect by adding 0.3 to 1.5 percent by weight to the semiconducting layer of manganese dioxide Has thallium oxide.

The amounts of the individual oxides mentioned below are percentages by weight of the mixture.

This is an oxide that has high conductivity but no self-healing properties Thallium oxide. The conductivity of a mixture of 5% thallium oxide and 95% natural manganese dioxide is ten times larger than that of pure natural manganese dioxide. The conductivity of a Mixture of 15% thallium oxide and 85% natural manganese dioxide is more than a hundred times Electrolytic capacitor

Applicant:

International Standard Electric Corporation, New York, N.Y. (V. St. A.)

Representative: Dipl.-Ing. H. Ciaessen, patent attorney,
Stuttgart-Zuffenhausen, Hellmuth-Hirth-Str. 42

Ronald Alfred Hill, Aldwych, London

(Great Britain),
has been named as the inventor

greater than that of natural manganese dioxide. At the same time are the self-healing properties this mixture is about the same as the pure natural manganese dioxide.

As an embodiment of the invention, a capacitor is described below, which is a sintered porous tantalum body as an anode. The advantages of the arrangement should be in terms of Drawings are explained in more detail in which

Fig. 1 shows the course of the loss factor with the frequency and

Fig. 2 shows the percentage change in capacitance with frequency. .

The inner surface of a sintered porous tantalum body is first created with a dielectric film of tantalum oxide by anodic treatment in a 60% sulfuric acid solution at 140 ° C., using a cathode made of platinum and a voltage of 18 Volts. In this way a capacitor for an operating voltage of 8 volts is obtained. The anodic hand-? Treatment continues until the current has dropped to approximately 200 microamps. This current value is characteristic of a cylindrical anode 7 mm long and 3 mm in diameter. The anode is then removed from the solution and washed thoroughly. It is then immersed in a solution of manganese nitrate with a specific gravity of 1.5, which contains thaUium nitrate at a concentration of 4.76 g per liter. When the anode is completely soaked with the solution, it is ^{heated for 15 minutes in air to 450 0} C, whereby the salts decompose and in the pores of the

109 689/187

At the anode an intimate mixture of manganese dioxide and thallium oxide is formed. This gives a coating of manganese dioxide that is 1.2 percent by weight Contains thallium oxide. Good results are obtained if the concentration of thallium oxide is between 0.3% and 1.5% by weight. At this concentration are the forming properties of manganese dioxide is present unchanged, but the conductivity is significantly increased. Thereafter the process of impregnation and decomposition is repeated and the anode is subsequently reformed in a 5% boric acid solution in the usual way.

The complete process step of the first impregnation and decomposition, the second impregnation and decomposition and reforming are then repeated a second time if necessary. Finally, conductive material, e.g. B. graphite, applied in the usual way to a To get cathode connection with low resistance. The anode is for this purpose, for example in exchanged for a colloidal graphite solution. On the graphite coating, the cathode is in the form of a metallic coating applied by spraying or melting, whereby it should be noted that the anode guide remains isolated from the cathode. The arrangement is then installed in a housing and in provided with anode and cathode connections in a known manner.

In Fig. 1 there are two curves for two 50 μΡ Κοη capacitors made of tantalum and shown with solid electrolyte for 8VoIt operating voltage. the Curve 1 was measured for a capacitor in which the semiconducting oxide consists exclusively of manganese dioxide and curve 2 for a capacitor in which the solid, conductive material consists of consisted of a mixture of manganese dioxide with 1.2 percent by weight of thallium oxide.

From the curves it can be seen that the loss factor due to the addition of thallium oxide drops from 55 to 28% at 1 kHz and from 90 to 84% at 10 kHz.

The addition of thallium oxide, however, has a second advantage. The capacity of sintered As is known, tantalum bodies depend on the particle size of the tantalum powder used. The lower the particle size, the larger the capacity of the sintered body per unit volume. When trying however, it was found that the capacitance thus increased at higher frequencies becomes less. This drop in capacity is due to the addition of thallium oxide in the mentioned Quantities decreased, as can be seen from FIG.

In Fig. 2, two curves for tantalum capacitors with solid electrolytes of 50 μΡ and 8 volts operating voltage are shown. Curve 3 'was obtained from a capacitor whose semiconducting oxide consisted only of manganese dioxide and curve 4 from a capacitor in which the solid conductive material consisted of manganese dioxide with an addition of 1.2 percent by weight of thallium oxide.

It can be seen from the curves that the drop in capacity due to the addition of thallium oxide from 9 to 2; 1% at 1 kHz and from 65.3 to 27.3% at 10 kHz.

It is therefore possible to add a certain percentage of thallium oxide capacitors produce with higher capacity per unit volume, their capacity drop at higher frequencies is less.

The thallium oxide can also be completely or partially replaced by cerium oxide. When making the Oxide mixture is used for this purpose, cerium nitrate. The operating voltage can be reduced by adding cerium oxide of the capacitor.

Although a porous tantalum body has been described as an anode as an exemplary embodiment, it is also possible another film-forming metal can be used, e.g. B. tungsten, hafnium, niobium, titanium or Zircon.

The application of the invention is not to capacitors with anodes made of porous sintered Metal is limited, but foils or wires can also be used as the anode.

For the anode, aluminum in the form of a foil or a wire can also be used instead of the above film-forming metals are used.

The invention is not limited solely to the illustrated and described exemplary embodiments.

Claims (4)

PATENT CLAIMS: 1. An electrolytic capacitor comprising an anode which is coated with a product obtained by anodic treatment dielectric film carrying a semi-conductive layer of manganese dioxide, which in turn is covered with an electrically highly conductive cathode, characterized in that the semi-conductive layer of manganese dioxide addition of 0.3 to 1.5 percent by weight of thallium oxide. 2. Electrolytic capacitor according to claim 1, characterized in that the anode consists of a porous body made of sintered metal. 3. Electrolytic capacitor according to claim 1 and 2, characterized in that the Anode made of one of the metals tantalum, tungsten, niobium, hafnium, titanium, zirconium or aluminum consists. 4. Electrolytic capacitor according to claim 1 to 3, characterized in that the Thallium oxide is partially replaced by cerium oxide. Considered publications:
French Patent No. 1091097;
U.S. Patents No. 1845067, 2005 279,
575, 2075 351, 2076905. 1 sheet of drawings © 109 689/187 9.