Publications

Abstract not provided.

The objective of this study was to determine if a distribution of pit induction times (from potentiostatic experiments) could be used to predict a distribution of pitting potentials (from potentiodynamic experiments) for high-purity aluminum. Pit induction times were measured for 99.99 Al in 50 mM NaCl at potentials of -0.35, -0.3, -0.25, and -0.2 V vs. saturated calomel electrode. Analysis of the data showed that the pit germination rate generally was an exponential function of the applied potential; however, a subset of the germination rate data appeared to be mostly potential insensitive. The germination rate behavior was used as an input into a mathematical relationship that provided a prediction of pitting potential distribution. Good general agreement was found between the predicted distribution and an experimentally determined pitting potential distribution, suggesting that the relationships presented here provide a suitable means for quantitatively describing pit germination rate.

High-purity aluminum samples were implanted with 35 keV Cl{sup +} then polarized in both Cl{sup -}-containing and Cl{sup -}-free electrolytes in order to ascertain corrosion behavior as a function of Cl{sup -} content in the oxide. Implant fluence between 5 x 10{sup 15} and 2 x 10{sup 16} Cl{sup +} cm{sup -2} resulted in little or no localized attack. Implant fluences of 3 x 10{sup 16} and 5 x 10{sup 16} Cl{sup +} cm{sup -2} resulted in significant pitting in a Cl{sup -}-free electrolyte with the severity scaling as a function of implant fluence. The low variability in the pitting behavior of the 5 x 10{sup 16} Cl{sup +} cm{sup -2} sample suggests that this implant dosage results in a critical Cl{sup -} concentration in the oxide for pit nucleation. The passive current density (i{sub pass}) decreased with increasing implant fluence. A space-charge effect is proposed to account for this phenomenon, although effects from defect interactions and possible oxide thickening are still under consideration.

Abstract not provided.

Abstract not provided.

Engineered Cu-rich islands were fabricated on an Al thin film to investigate pit initiation mechanisms at noble particles. X-ray photoelectron spectroscopy confirms that the thin film Cu-rich islands interdiffuse with the underlying Al substrate to form Al{sub 2}Cu islands. The defect arrays exhibit open circuit potential fluctuations whose magnitude and frequency increase as defect spacing decreases for constant island size and cathode/anode ratio. Post-exposure examination by energy dispersive spectroscopy (EDS) shows that the Al beneath the Cu-rich island dissolves with a crevice geometry. Engineered Al islands fabricated under identical conditions do not induce crevice corrosion in the vicinity of the Al defects. These results suggest that the Al dissolution is driven by the galvanic coupling between the noble island and matrix, and/or by a local change in chemistry, rather than by the presence of a defective oxide in the vicinity of the island.