Effect of Etch Tunnel Length Distribution on Frequency Dispersion of Pure Aluminium Foil Used for Aluminium Electrolytic Capacitor

摘要

The present work involves the effect of etch tunnel length distribution on frequency dispersion of pure aluminium foil used for aluminium electrolytic capacitor by using scanning electron microscopy and electrochemical impedance spectroscopy. Etching was carried out under galvanostatic polarization as a function of etching time to control the etch tunnel length distribution. Then the specimen was anodized in a 0.5 M H_3BO_3 + 0.05 M Na_2B_4O_7 solution at 0.5 mAcm~(-2) up to 50 V and held at 50 V for a further 30 min. The etch tunnel length distributions were characterized roughly with the help of scanning electron microscopy after dissolving aluminium by immersing in a bromine-methanol solution. In the present work, transmission line model was modified taking into account the presence of the length distribution of aluminium etch tunnels on the assumption that fraction of tunnels dying per unit time holds constant. From the experimental results, it was revealed that the tunnel length was more widely distributed with increasing etching time. At the same time, the similar trend in shape was also observed between the impedance spectra experimentally measured and those spectra numerically simulated, indicating that the impedance spectra of the anodized aluminium foil can be analysed on the basis of the transmission line model.