Ultrasonic-assisted ac etching of aluminum foils for electrolytic capacitor electrodes with enhanced capacitance

ac etching of high-purity aluminum foils in hybrid acids including hydrochloric acid, sulphuric acid and oxalic acid was investigated and the effects of ultrasonic-assisted stirring on the performances of the etched foils were investigated in this work. Scanning electron microscopy (SEM) was used for observation of the etched foils. Compared with the classically used mechanical stirring (magnetic stirring), the assistance of ultrasonic increased the performance of the etched foil. With 20 V forming voltage, the static capacitance and bending strength of the foils etched with ultrasonic stirring reached 76.5 μF cm−2 and 98 times compared with 71.2 μF cm−2 and 85 times respectively for the foils fabricated with magnetic stirring using 100 μm aluminum foils. The performance enhancement with the assistance of ultrasonic is probably due to the cavitation effects which are beneficial for the remove of protective layer and the dispersion effects which reduce concentration polarization in the bulk etchant solutions.