CS269740B1 - Process for preparing manganese dioxide layers on solid supports - Google Patents

Abstract

The application of manganese dioxide to solid substrates, especially to positive electrodes of electrolytic capacitors, is improved by thickening the manganese salt solution by adding silica or silicic acid-based substances to a consistency suitable for application, e.g. by screen printing or dipping. As additives, e.g. hydrolyzed ethyl silicate, silica aerosol or a mixture thereof can be used.

Description

High-quality electrolytic capacitors consist of an anode made of aluminum or tartal, the surface of which is covered with an oxide layer, which serves as a working dielectric, and a cathode layer, the main component of which is a layer of manganese dioxide Mn0 _2. This layer is usually prepared by repeatedly applying a solution of manganese nitrate and its thermal decomposition. Electrolytic capacitors with a tantalum anode usually contain an anode made of sintered tantalum, and therefore porous; its saturation with a manganese nitrate solution is therefore relatively easy. In contrast, electrolytic capacitors with an aluminum anode usually contain an anode made of smooth sheet metal, to which the concentrated manganese nitrate solution adheres only poorly.

Therefore, in order to create well-adhering and homogeneous layers, the application of manganese nitrate must be repeated many times. For example, patent DE No. 2,623,592 mentions a total number of layers of up to 10. The disadvantage of the process is the high thermal stress on the substrate during the repeated decomposition of manganese nitrate.

Another way is to thicken the manganese nitrate solution with a suitable additive so that it adheres well even to a smooth metal substrate and can be applied by screen printing in the production of thick-film and hybrid integrated circuits. The additive must be miscible with water or wettable by aqueous solutions. Furthermore, the decomposition temperature of manganese nitrate is about 250 to 400 °C. The additive or its thermal decomposition products must not interfere with the manganese dioxide at these temperatures, for example by its reducing effects or excessive gas evolution or foaming. For this reason, the vast majority of binders and thickening additives of organic origin are not suitable.

The above disadvantages are eliminated by the method of preparing manganese dioxide layers. The subject of the invention is the solution of this problem according to the invention, the essence of which lies in the fact that one or more additives based on silicon dioxide or silicic acid are added to the manganese nitrate solution, which are colloidal or in the form of water-wettable ultramicroparticles. None of these additives at the temperature of the conversion of manganese nitrate to manganese dioxide does not disrupt the resulting layer and at the same time facilitates the application to the substrate.

For example, silica aerosol particles or the decomposition product of silicic acid esters (or a mixture thereof) can be advantageously used, or mixtures with other substances that, in addition to their original purpose, also thicken the consistency of the mixture containing manganese nitrate. Such substances include, for example, carbon, electrically conductive carbon black, manganese dioxide or powdered silver or other metals.

By choosing the concentration of the aforementioned additives, it is possible to obtain a mixture of the consistency required for the selected application method, for example by dipping, spraying, vacuum impregnation or screen printing.

Example 1 ·

Anodes made of aluminum sheet, prepared in a known manner by activating their surface, electrochemically etching and shaping, are immersed in a solution containing 15 to 60 wt. % of manganese nitrate and 5 to 20 wt. % of a mixture prepared from 30 ml of ethyl silicate, 80 ml of ethyl alcohol, 5 ml of water, 1 ml of ethylene glycol and 0.1 ml of nitric acid. The anodes are then removed, dried with a stream of hot air, dried in a hot-air dryer and annealed at 250 to 400 °C. The process of soaking, drying and annealing is repeated two to four times; finely ground graphite can be added to the manganese nitrate solution in an amount of 20 to 150% of the amount of manganese nitrate. The manganese dioxide layer thus formed adheres well to the substrate, has good electrical conductivity and fills the unevenness of the anode surface well.

Example 2

Surfaces covered with zo> were formed on a ceramic substrate in a known manner;

CS 269 740 Bl of tantalum, forming the anodes of the capacitors. Cathodes were screen-printed on them from a layer of manganese dioxide using a paste of 60% manganese dioxide nitrate solution, 15% of a mixture containing hydrolyzed ethyl silicate according to the previous point, 8% silica aerosol and 50% ground graphite. The cathodes were dried with hot air and in a hot air dryer at 120 °C and annealed at 300 to 400 °C. Finally, the cathodes were provided with a cathode terminal.

Claims (4)

SUBJECT OF THE INVENTION 1. A method for preparing manganese dioxide layers on solid substrates, characterized in that a layer of a manganese salt solution with the addition of substances containing ultramicrodisperse silicon dioxide, silicic acid or a mixture thereof is applied to the substrate. 2. The method according to item 1, characterized in that a silica aerosol is used as the ultramicrodispersed substance. 3. The method according to item 1, characterized in that the ultramicrodispersible substance used is a product of hydrolysis of silicic acid ester. 4. The method according to items 1 to 3, characterized in that the manganese salt solution contains finely divided carbon, manganese dioxide, graphite or powdered metal or a mixture of these substances.