2003 Volume 52 Issue 8 Pages 416-420
Aluminum electrolytic capacitors have the tendency that alkali substance gradually concentrates on the cathode terminal end, regardless of load or unload condition. At the time, if the electrolyte consists of the salt containing strong alkali substance such as quaternary alkyl ammonium, the sealing may be affected in the performance.
We investigated the mechanism generating the concentration of the alkali substance. As the result, the obvious difference in electrochemical characteristic difference between two electrode materials, aluminum cathode foil and tab, which are used for the cathode terminal end of the capacitors causes this concentration. Basically, the cathode foil and the tab with different spontaneous potentials each other form a galvanic couple. And the alkali substance comes to concentrate around the cathode terminal end, due to the cathodic reaction which occurs on the tab surface with comparatively noble potential. The reason why the two electrode materials having similar aluminum purity show the obvious difference electrochemically is considered due to the high purification of the aluminum foil surface during etching process of foil.