DC etching of aluminum is used in the fabrication of electrodes to enlarge the surface area of the aluminum base plate, thereby increasing its capacitance. To clarify the basic mechanism of this etching process, in situ
monitoring was attempted using a photoacoustic (PA) technique. The base plate was 99.99% aluminum foil, the electrolyte was an aqueous solution 2mol/dm3
. Etching was done under galvanostatic conditions at 80°C. The light source for the PA technique was an Ar ion laser beam that was chopped mechanically. A PA signal from a piezoelectric transducer attached to the rear surface of the working electrode (Al) was detected by a lock-in amplifier.
Changes in the PA signal over time suggests information about the initial roughness of the surface, the growth of etching pits and the penetration of the pits through the foil. The current density at which etching was carried out changed the behavior of the PA signal. The process of etching was confirmed ex situ
by SEM and optical microscopy. The above data yielded in situ
information about the DC etching process.