Interpretation of potential transients during aluminum etch tunnel growth in the presence of sulfuric acid

When sulfuric acid is added in an etching solution of 1 M hydrochloric acid, the effect of the sulfate ions on the aluminum etch pit formation and tunnel growth was investigated with the morphology study and current interruptions in applied etching current. Initial potential transient supports that sulfate ion works as a film forming agent and inhibits the pit initiation during the anodic current etching. Observation of ruptured oxide films suggests that cathodic hydrogen evolution can take place inside the pits. Current step reduction and cathodic pulse superimposition experiments indicate that the actively dissolving tunnel tip surface is covered with aluminum chloride salts and sulfate ion moves far behind inside tunnels during the tunnel growth.