Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Kurt R. Hebert

Abstract

Passivation of corroding surfaces in aluminum etch pits and tunnels was investigated by step reductions and cathodic pulses in applied etching current. Morphology study shows that, in the early stage of passivation, the corroding surface consisted of recessed patches, which are actively dissolving surface, and flat passive area. These active patches are found within the potential range between the potential of zero charge (E[subscript]PZC) and the repassivation potential, and the actively corroding area increases with potential, from zero near E[subscript]PZC to the entire surface at the repassivation potential. A mathematical model describing the progress of passivation was developed and compared to experimental measurements. The calculation indicated that patchwise passivation takes place in times less than 100 [mu]s and the fractional active area is a function of potential below the repassivation potential. It thus suggests that the patches are islands of specifically adsorbed chloride ions, so that the passivation is controlled by desorption of these ions. For cathodic current pulses, the effect of pulse time and current pulse ratio on passivation and pit nucleation was investigated through the morphological study of actively dissolving tunnel tip surface and accompanying potential transients.

DOI

https://doi.org/10.31274/rtd-180813-11954

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Yongsug Tak

Language

en

Proquest ID

AAI9321214

File Format

application/pdf

File Size

172 pages

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