Effects of Waveforms on Pitting Behavior of Aluminum Foil During AC Etching

Aluminum foil used as the anode of low-voltage capacitors were etched in hydrochloric acid using an alternating current (AC) to investigate how the current waveforms affect the pitting behavior of the foil. The voltage/current relationship at a specific cycle was measured via a galvanostatic voltammetry polarization (GVP) method.  The surface morphology of etched foil of which the etch films had been removed was observed using SEM.  Finally, cross-sectional TEM was employed to characterize the coalescence and propagation of the pits, as well as the microstructure and thickness of the etch film. In this study, using the square current waveform to etch the foil suffered the greatest mount in weight loss and consisted of the largest and deepest pits that were covered with relatively thick etch films. Meanwhile, GVP shows that during each cycle the total charges expended in the dissolution of the foil were larger for the square waveform than that of the triangular and sinusoidal waveforms. Based on microstructural characterizations and GVP measurements, possible mechanisms regarding the nucleation, growth, coalescence and propagation of the pits are discussed in details.

Keyword: galvanostatic voltammetry polarization (GVP) curve, low-voltage capacitors, weight loss, current waveforms.