Study of Single Al Corrosion Pit Growth By Electrochemical Techniques
For stable Al pit growth, it is widely accepted that local pit chemistry and environment are critical; or a critical value of the stability product (x.i), where x the pit depth, and i the current density, must be maintained for pit survival [2-6].
Several techniques have been proposed for studying pit growth rates, including (1) Use of artificial pit (“lead-in-pencil”) electrode; (2) Single pit formed by implantation; laser irradiation; (3) Think film electrode  ; (4) The foil penetration technique .
In this work, we propose to employ a single Al wire (~100um dia.) mounted in epoxy with different initial pit depth d, which is produced by anodic dissolution, for singe Al corrosion pit growth by coupling with a large Al foil ring as its remote cathode through a zero resistance ammeter (ZRA), as schematically shown in Fig.1. The purpose of this study is, in combined with in-situ scanning vibrating electrode technique (SVET, Fig. 2), to determine quantitatively whether the single Al corrosion pit growth follows a depth-dependent growth model as often predicted.
This work was performed under United Technologies Corporate R&D funding.
Fig. 1 Schematic geometry of single al corrosion pit formed by an Al wire mounted in epoxy, by coupling with a large Al foil ring as its remote cathode through a zero resistance ammeter (ZRA).
Fig. 2 In-situ SVE images of single Al corrosion pit growth, showing transition from (a) open circuit condition (before coupled) to (b) galvanically coupled condition.
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