Length Scales in Alloy Dissolution

Arizona State University, Scottsdale AZ

Investigators

Abstract

This grant involving Arizona State University (Sieradzki) and Virginia Tech. (Corcoran) explores the fundamental physics and materials science of nanoporous metal evolution via an alloy dissolution process known as dealloying. The research aims to differentiate among several recent theories of dealloying by examining the role of pre-existing length scale on porosity evolution and the electrochemical parameters such as the critical potential, characterizing this process. In order to access the role of pre-existing length scale in the pattern formation process, the de-alloying behavior of fixed composition alloys with artificially tailored and tunable microstructures will be studied. Two types of microstructures will be examined: tunable spinodal microstructures (Ag-Ni and Au Ni alloys) and compositionally modulated superlattices (Ag-Ni, Au-Ni and Au-Ag alloys). These behaviors will be compared to that of single-phase solid solution alloys (e.g., Ag-Au) that also have a pre-existing length scale (percolation cluster structure) determined by alloy composition. In addition to standard electrochemical, x-ray, and electron microscopy characterization, in situ small angle neutron scattering (SANS) will be used to determine, in real time, the evolution of the nanoporous microstructures. Measurements will be performed using both the 8 and 30 meter long SANS instrument at the National Institute of Standards and Technology. The long-term goal of this effort is to use the understanding of the underlying mechanisms to produce nanoporous metals in a variety of forms compatible for example with thin film silicon-based architectures. The dealloying method for producing porous metals is extremely versatile in that the size scale of the porosity can be precisely tuned in the range of 3 nm to greater than 10 mm. The electrodes can be produced in virtually any geometry including bulk and thin film form. Multiple length scales and graded structures can be produced to precisely tailor electrode performance depending upon the application. As such, the applications of such materials are broad and encompass such areas as filtration, ultra-high surface area electrodes for batteries and fuel cells, catalysts, and sensors, particularly in biochemical applications. The proposed effort has broad impact to the education of undergraduate and graduate students, development of technology for use in such areas as medical technologies that will benefit society at large, and development of basic science to impact the scientific community across many fields of materials science.