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This paper reexamines the concept of the dealloying critical potential by considering the critical potential to be a kinetically controlled morphological transition dependent not only on extensive system parameters such as alloy and electrolyte composition, but also on the rate of application of an intrinsic parameter such as the potential ramp rate. In the limit of a quasi-static potential sweep rate, an expression for the critical potential is derived which considers both compositional and morphological fluctuations on the alloy surface at the incipient point of either stability ͑passivation͒ or instability ͑bulk dealloying͒. In addition, we present detailed critical potential results for the entire range of Ag-Au alloy compositions in x M AgClO 4 ϩ 1 M HClO 4 and x M AgNO 3 ϩ 1 M HNO 3 ͑x ϭ 10 Ϫ4 , 10 Ϫ3 , 10 Ϫ2 , 10 Ϫ1 , and 1͒. These results are shown to be consistent with the expression for the critical potential. Finally, we present and discuss ancillary experiments examining the effect of potential sweep rate on the determination of the critical potential.

This work is aimed at developing a protocol based on surface limited redox replacement (SLRR) of underpotentially deposited (UPD) Pb layers for the growth of epitaxial and continuous Pt thin films on polycrystalline and single crystalline Au surfaces. Different from previously reported papers using SLRR in multiple immersion or flow cell setups, this work explores the one-cell configuration setup as an alternative to improve the efficiency and quality of the growth. Open circuit chronopotentiometry and quartz-crystal microbalance experiments demonstrate steady displacement kinetics and a yield that is higher than the stoichiometric Pt(II)-Pb exchange ratio (1:1). This high yield is attributed to oxidative adsorption of OH(ad) taking place on Pt along with the displacement process. Also, ex situ scanning tunneling microscopy surface characterization reveals after the first replacement event the formation of a dense Pt cluster network that homogenously covers the Au surface. The Pt films grow homogenously with no significant changes in the cluster distribution and surface roughness observed up to 10 successive replacement events. X-ray diffraction analysis shows distinct (111) crystallographic orientation of thicker Pt films deposited on (111) textured Au thin films. Coarse energy dispersive spectroscopy measurements and finer X-ray photoelectron spectroscopy suggest at least 4 atom % Pb incorporating into the Pt layer compared to 13 atom % alloyed Cu when the growth is carried out by SLRR of Cu UPD.

We present results of a comprehensive electrochemical study aimed at determining the factors that control the corrosion evolution of the important structural alloy Al 2024-T3. An important aspect of corrosion in this alloy is copper redistribution. The redistributed copper serves to enhance the kinetics of the corrosion process and presents some major difficulties with respect to development of new families of conversion coatings. Two major sources of “mobile” copper are discussed, the Al2normalCuMg S-phase and copper in solid solution. In each case, a dealloying mechanism is responsible for liberating copper that becomes available to redistribution by solid state and/or liquid phase transport mechanisms. This work is concerned with identifying the relative importance of these sources of copper and the active transport mechanisms. In order to decouple the sources of copper, we designed “synthetic” 2024 alloys that emulate the oxygen reduction kinetics of the real alloy. Our results indicate that, in principal, both sources of copper are operative during redistribution and, for the particular alloy that we examined, both contribute about equally to the amount of redistributed copper. © 2002 The Electrochemical Society. All rights reserved.

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