Fast Impedance Analysis of a Surface Microstructure during Anodic Oxidation of a Copper/Gold Alloy

Abstract

The anodic oxidation of ordered Cu/Au alloys was studied by quartz crystal microbalance measurements and quartz crystal impedance spectroscopy. A fast impedance measurement technique is presented, which allows us to monitor the surface microstructure during the selective dissolution. We learn that the state of the alloy surface characterized by impedance measurements after the oxidation is not necessarily equal to that during the oxidation.

Selective Dissolution below the Critical Potential and Back Alloying in Copper-Gold Alloy

“…7,10,11,21,[27][28][29] There are now data suggesting that the product layer at the alloy surface is in a much different ͑lower density͒ state during dissolution than it is during recovery after cessation of the experiment, and that the two processes are associated with two different time scales. 19,25 Scanning tunneling microscopy ͑STM͒ 7,10,21 and transmission electron microscopy ͑TEM͒ 9 measurements by various authors support the long-held view that the alloy surface remains essentially planar during selective dissolution below E c . [1][2][3][4][5][6] The objective of this paper is to characterize the Au-rich product layer that forms during the selective dissolution of Cu from Cu-Au alloys at potentials below the critical potential.…”

“…17 On the other hand, the mechanisms that lead to selective dissolution from a planar surface below E c , and dealloying above E c , are the subject of considerable debate. [2][3][4][5][6][7][8][9][10][11][12]15,[18][19][20][21][22][23][24][25][26] The subject has been reviewed before [4][5][6] and is still attracting considerable attention.…”

“…The Cu-Au alloy system has often been taken as a model system for dealloying studies. [1][2][3][7][8][9][10][11][12]18,19,21,[23][24][25] In this work the Cu-depleted surfaces were characterized ex situ using TEM to examine Cu-Au samples that had undergone both the selective dissolution of Cu for various times at E Ͻ E c and the back alloying ͑current-off͒ processes. The current transients were recorded during the anodic dissolution of Cu from the alloy.…”

Environmentally Induced Failure of Gold Jewelry Alloys

“…A time-dependent solid-solution enrichment process of the noble metal in this layer has previously been reported based on Auger spectroscopy of anodically dissolved CuAu (16) and CuPd (17) alloys below E c . During the selective dissolution process, the Au-enriched layer is less dense than the parent material (18,19). Thus the corrosion rate based not only upon the alloying elements but also the percent Au present in the alloy.…”

Quartz Crystal Microbalance Expanded Capability for Studying CuCl Crystal Formation on Copper Surfaces

“…For calibration purposes, we measured F and P for smooth electrodes contacting different Newtonian, aqueous sucrose solutions (Figure 1). Changes of F and R ′ (or, equivalently, P ) depend on the product of the solid/liquid contacting area, A ,6, 7 and ( ρη ) 1/2 ,8, 9 where ρ and η are the density and the viscosity of the solution, respectively.…”