SEDL / STP / STP1188-EB / STP18065S

The Characterization of the Coarsening of Dealloyed Layers by EIS and Its Correlation with Stress-Corrosion Cracking

Kelly, RG
Research assistant professor, University of Virginia, Charlottesville, VA

Young, AJ
Research student and reader, Corrosion and Protection Centre, University of Manchester Institute of Science and Technology, Manchester,

Newman, RC
Research student and reader, Corrosion and Protection Centre, University of Manchester Institute of Science and Technology, Manchester,

Pages: 19    Published: Jan 1993

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Abstract

The origin of the reversibility of the environmental embrittlement of an Ag-20 at. % gold alloy in 1 M HClO⁴ has been investigated. The structure of the porous gold layer formed on this alloy under potentiostatic polarization has been studied by electrochemical impedance spectroscopy (EIS). In the as-dealloyed state, a 50-μm layer has impedance behavior electrically equivalent to a layer containing 10¹¹ cylindrical pores/cm² (geometric area) each with a radius of 9 nm. Upon aging, the pores closest to the substrate coarsen first, destroying the ability of the layer to inject a brittle crack into the uncorroded substrate. This change in structure is observable as a change in the low-frequency portion of the impedance spectrum. The observed potential dependence of this coarsening indicates that it occurs due to surface diffusion of gold atoms.