The effect of transducer to electrode distance and acoustic power on the etching of high-purity aluminum foil

초록

In the manufacturing of aluminum electrolytic capacitors, high-purity aluminum foils are anodically etched to prepare a high surface area. Ultrasound is well known for increasing mass transfer in electrochemical process. The acoustic cavitation increases the corrosion of the metal and promote passivity breakdown particularly in aggressive media. The effects of transducer to electrode distance and acoustic power on the galvanostatic etching of aluminum foils in an ultrasonic field at 68kHz were investigated. Measurement of electrostatic capacitance showed clearly the effects of aluminum pretreatment and ultrasonic etching. The high-purity aluminum foils (thickness 110㎛, purity 99.99%, Tokai, Japan) for etching was used as the working electrode. Galvanostatic etching was carried out using a potentiostat/galvanostat (EG&G PAR 273A). An Ag/AgCl/4N KCl reference electrode was used, along with a Pt wire on a counter electrode. All experiments were performed at a constant ultrasonic frequency of 68kHz (Woosung ultrasonic co, Ltd). Potential transients were recorded with digital oscilloscope (Tektronix, TDS350). Surface morphology was observed with scanning electron microscope (SEM, Hitach S-4300 & 4200). Capacitance was measured with LCR meter (ANDO, Type AG-4303). The Analysis of the surface morphology of etched tunnels by SEM indicated that appropriate acoustic power resulted in higher pit density and longer etched tunnels, compared to conventional aluminum etching method.