Repassivation of Pits in Aluminum Thin Films

Abstract

The effect of metal film thickness on repassivation of pits in sputter-deposited Al thin films was investigated in chloride solutions. The repassivation potential and the critical current density, which is the pit current density below which pits stop growing, were determined for pits in Al thin films ranging from 100 Ǻ to 43 µm in thickness. The repassivation potential first decreased as thickness increased from 100 to 4350 Ǻ, and then increased as the film thickness increased further. This behavior was found to be a consequence of the pit currentdensity/potential relationship. The critical current density, a more informative parameter, decreased for increasing metal film thickness, even when the repassivation potential increased. The critical current density is the minimum current density needed to maintain the critical pit environment and prevent repassivation. The repassivation potential for a given metal film thickness is the potential at which the pit current density drops below the critical value. Masstransport and ohmic resistance both increase as the metal film thickness increases, but the former enhances pit stability and the latter destabilizes pitting in this system. Pit repassivation, and thus stability, are strongly influenced by mass-transport considerations for pits in very thin pits, even though dissolution at low potentials is not under pure mass-transport control. Ohmic effects become increasingly important as the film thickness increases.

Effects of environmental factors on key kinetic parameters relevant to pitting corrosion

“…After reaching the plateau value, the repassivation potential becomes invariant of pit depth. Similar reports [16,34,41,42] on different materials showed a similar lack of sensitivity of repassivation potential to pit depth when large amounts of charge were passed to grow the pits and hence defining the lower bound in potential which can sustain pit growth. As shown in Fig.…”

Metal Dissolution Kinetics in Aluminum Etch Tunnels

“…In experiment set (1) the patch area during t H is varied, while the total patch current is fixed, while in set (2) the patch area is constant, and the current during the anodic pulse is varied. Since the data for sets (1) and (2) appear to follow the same trend, the dependence of the patch current density on the potential is the same for both the current and area variations. Thus, the active electrode area is identified correctly as the patch area.…”

“…1,4 They measured the dissolution and total current densities of the pit with use of microscopic observation of the evolution of pit geometry. The dissolution current density was found to increase with potential and decrease with film thickness, with the data for various films following separate trends when plotted vs. potential.…”

“…2,3 Frankel and co-workers investigated the growth of two-dimensional pits in thin aluminum films and noted a potential region above the pitting potential in which the pit current increased with potential, and at higher potentials a current plateau which was ascribed to mass-transport limited dissolution. 1,4 Like Hunkeler and Böhni, they concluded that the first region was controlled by ohmic resistance. Beck's studies of artificial pits in concentrated AlCl 3 solutions also revealed ohmic-controlled dissolution with mass transport control at very high potentials (greater than 5 V vs. saturated calomel electrode).…”

Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

“…The presence of any Cr on the surface of the untreated electrode or any change in its properties would be a result of migration of a Cr species from the CCC-coated sample. Pit growth in thin metallic films deposited on inert substrates has been found to be an interesting approach to the study of pit growth [8][9][10][11][12]. Details of the experimental approach are available in the previous publications [8][9][10][11][12].…”