Studies on the Chemical Etching Mechanism of Aluminum in an Acidic Bath by the AC Impedance Method

Abstract

Chemical etching of Al in an acidic bath was studied by measuring the etching rate and the AC impedance of Al in the bath. The etching rate increased with increasing bath temperature. Moreover, the rate was significantly increased by the addition of Fe³⁺ ions and phosphoric acid into the bath. The mechanism of the etching reaction was then studied. In the case of the Fe³⁺ ion additive, it was found that the Fe³⁺ ion not only oxidize the Al, but also accelerate the reaction rate of H⁺ reduction. Changes in bath temperature mainly affected the reduction rate of H⁺ ions, which made up 82% of the etching reduction rate, while that of Fe³⁺ ions made up 18%. In the case of the phosphoric acid additive, the enhancement mechanism of etching rate acceleration was attributed to a dissolution reaction of the Al oxide film.