Gallium enrichment and film detachment during anodizing of an Al-Ga alloy

Al-0.028 at.% Ga alloy, either just electropolished or subsequently anodize d, was examined for gallium enrichment in the alloy using Rutherford bucksc attering spectroscopy. Unlike with alkaline etching, no significant enrichm ent of gallium, namely <5 x 10(17) Ga atoms m(-2), was developed by electro polishing in perchloric acid:ethanol, which is suggested to be associated w ith activation of the alloy in the acid bath. In contrast, during anodizing in ammonium pentaborate electrolyte, gallium is accumulated to 400 V at 50 A m(-2) progressively in a thin alloy layer beneath the anodic film, with initial formation of essentially gallium-free alumina. The number of galliu m atoms accumulated in the enriched alloy layer per. unit area of alloy/fil m interface increases linearly with the anodizing voltage at 1.0 x 10(16) G a atoms m(-2) V-1. At anodizing voltages above similar to 150 V, the films become detached locally from the alloy. The detachment evidently coincides with the formation of fine voids at the alloy/film interface, observed in t he transmission electron microscope, possibly initiated by localized oxidat ion of gallium-rich regions of alloy. (C) 2000 Elsevier Science Ltd, All ri ghts reserved.