Metal dissolution kinetics in aluminum etch tunnels

The potential dependence of the metal dissolution current density of alumin um in etch tunnels was measured, using pulsed increases of current during g alvanostatic etching experiments. Etching was carried out in 1 N HCl soluti on at 65 degreesC, and was followed by analysis of the topographic developm ent of the dissolving surfaces using scanning electron microscopy. By manip ulation of the current waveform, the dissolving area and the applied curren t were varied independently Parallel experiments with current interruptions were used to help identify the area of the dissolving surfaces during the anodic pulse, which were shown to be submicron size patches on the tunnel t ip surfaces. After correction for solution-phase potential drops, the curre nt was found to obey an exponential Tafel dependence on potential. Measurem ents of the dissolved depth vs. time show that the rate of cathodic hydroge n evolution is significantly increased during the anodic pulse, by comparis on with that at the more negative potentials during constant current etchin g. Good agreement of the present current-potential relation was obtained wi th that derived from the measurements of pit currents in thin films by Fran kel et al. [J. Electrochem. Sec., 143, 1834 (1996)]. (C) 2000 The Electroch emical Society. S0013-4651(00)02-012-7. All rights reserved.