De-alloying kinetics of an Au-based amorphous alloys

The process of de-alloying, i.e. removal of a less noble metal from an alloy, is applied here by electrochemical means to a Au-based metallic glass, Au40Cu28Ag7Pd5Si20, as a function of potential, temperature, and time. Very fine crystals nucleate with random orientation at the solid–electrolyte interface forming ligaments. The resulting material is constituted by ligaments made of pure Au and pores of smaller size whose dimensions coarsen up as a function of time to slightly above two hundred and below one hundred nanometers, respectively. The microstructure is uniform on both surfaces and across the ribbon. The extent of de-alloying is measured by monitoring the heat of crystallisation of the remaining amorphous phase giving linear trend vs time suggesting the reactions occur on continuously renewed surfaces.

Figure optionsDownload as PowerPoint slideHighlights
► Au-based amorphous ribbon dealloyed electrochemically.
► Thickness of dealloyed Au layer studied as a function of time.
► Dealloyed fraction obtained by DSC measurements.
► Random nucleation of Au crystals revealed by TEM.
► Ligaments and pores coarsen with time.