Examination of the metastable and stable pitting corrosion of aluminum modified with carbon by ion beam techniques

It is well known that aluminum and aluminum alloys are sensitive to pitting corrosion when exposed to aqueous solutions containing aggressive anions l ike halides. The destructive nature of pitting is due to its high local dis solution rates at electrode potentials above the so-called pitting potentia l U-p. Recently, it has been realized that also at potentials below U-p, in the passive and cathodic regions and around the free corrosion potential, anodic current transients appear which have been attributed to metastable p itting events. For the purpose of full characterization of the pitting beha vior, a program routine has been developed where the occurrence frequency, lifetime and rate of metastable pitting events are extracted from potentios tatic current/time-measurements depending on the electrode potential. The r outine has been applied to measurements of carbon modified pure aluminum. C arbon modifications were done with carbon evaporation and carbon sputtering under concurrent argon ion bombardment. The results are discussed in terms of the applied modification technique, their parameters and their effects on the corrosion protection ability of aluminum modified by carbon. (C) 200 1 Elsevier Science B.V. All rights reserved.