DE1122177B - Process for the production of roughened electrodes, in particular aluminum electrodes for electrolytic capacitors - Google Patents

Description

Process for the production of roughened electrodes, in particular aluminum electrodes for electrolytic capacitors The problem of roughening anode foils or the like. for electrolytic capacitors is well known, and its solution is already a very large number of proposals have been made which the conditions the degradation of aluminum or another valve metal according to the most varied Directions were varied. So were z. B. the most varied concentrations of acids used, the temperature of the etching baths was varied, the etching electrolyte All sorts of metal salts were added, and eventually it became pure chemical process of etching replaced or supported by anodic etching degradation of the valve metal by applying a positive voltage to the electrode to be etched was placed in the bath electrolyte.

In-depth investigations and tests have now shown that the The structure of the metal surface that occurs during the etching degradation depends largely on the speed and duration of the removal is dependent. The resulting knowledge makes The present invention takes advantage of the suggestion that the electrodes are first placed in an etching bath, in which as a result of slow metal degradation coarse blocks arise on their surfaces, and that afterwards the electrodes in one Etching bath are treated in which as a result of a rapid removal of these blocks a finely divided, deeply fissured relief is created, with the treatment time im first etching bath is a multiple of the treatment time in the second etching bath. the The above-mentioned experiments have shown that the dissolution of the metal in strong concentrated acid at high temperature and / or - at the above-mentioned anodic Etching - with a very high current density to a finely divided, deeply fissured relief leads, while removing an equal amount of metal under weaker conditions, z. B. in acid of lower concentration, at room temperature or at lower Current density or even currentlessness creates relatively large blocks. the The size of the blocks produced during the etching degradation can be determined by defining the etching conditions vary within certain limits and, as already mentioned above, it is advisable to start with with a slow removal rate and then in a second etching process to etch higher removal rate. During the etching process with a low removal rate, in the case of relatively coarse blocks with edge lengths over about 1 #t up to around 10 #t arise, so weak acids, especially weak hydrochloric acids, low temperatures, especially room temperature, but preferably long etching times used; in the subsequent etching process with a rapid removal rate, given by the amount of metal removed per unit of time, take place its highly concentrated acids, especially hydrochloric acids, increased temperatures of preferably about 80 ° C, highly corrosive metal salts in the electrolyte and / or high current densities with preferably only a short etching time of fractions used from one minute to a few minutes.

This new etching process is especially important where it is the production of highly roughened aluminum foils of a high degree of purity is about 99.99% or more. Recommended for such high-purity aluminum foils it is the proportion of metal salts in the successive etching baths and / or to vary the etching current density per unit area of the surface to be roughened, in such a way that in the etching process with the slow metal degradation, the current density small and / or the proportion of metal salts is small or equal to zero in the etching process with the rapid degradation, however, the current density and the proportion of metal salts are large are.

Claims (6)

PATENT CLAIMS: 1. Process for the production of roughened electrodes. in particular aluminum electrodes, for electrolytic capacitors, in which the electrodes treated in more than one caustic bath are characterized by that the electrodes are first placed in an etching bath, in which as a result of a slow metal degradation coarse blocks appear on their surfaces, and that afterwards the electrodes are treated in an etching bath, in which as a result of a rapid Removal of these blocks creates a finely divided, deeply fissured relief, whereby the treatment time in the first etching bath is a multiple of the treatment time in second etching bath is. 2. The method according to claim 1, characterized by the use initially an acid of lower concentration for slow metal degradation and then an acid of higher concentration for rapid degradation. 3. Procedure according to Claim 1 or 2, characterized in that the temperature of the second bath higher than that of the first bath. 4. The method according to claim 1, 2 or 3, characterized characterized in that the proportion of the etching-assisting metal salts in the first Etching bath is smaller than in the second. 5. The method according to any one of claims 1 to 4, characterized in that the duration of the first etching process is greater than that the second. 6. The method according to any one of claims 1 to 5, characterized in that that the duration of the second etching process is only a fraction of a minute or a few Minutes. Considered publications: German Patent Specifications No. 695 770, 914 042; Swiss patents No. 170 212, 183 306, 183 310, 204 622, 206 533; French Patent Nos. 836 320, 910 036; British patents No. 399 400, 433 818, 489 884, 504 559; U.S. Patent Nos. 2180,798, 2,218 076, 2 396 685, 2 616 799.