SGER: Understanding Phase Diagrams of Small Metal Particles

University Of Virginia Main Campus, Charlottesville VA

Investigators

Abstract

TECHNICAL: Researchers seeking guidance as to phase stability, solubility limits, wetting criteria etc., have almost no guidance when the size scale of the alloy system being used is at the nanoscale. Researchers are only recently attempting to extend notions of using G-X diagrams from bulk alloys to provide guidance for T-X phase diagrams for nanoparticles. The thrust of the present SGER research is to take a fresh look at this problem both theoretically from a thermodynamic modeling point of view and experimentally by mapping the phase fields of isolated nanoparticles as a function of size r, temperature T, and composition X. The appropriate phase diagram for nanoparticles is one with these three axes. Experimentally nanoparticles will be formed in an ultra high vacuum chamber by either physical vapor deposition, electron beam sputtering, or pulsed laser deposition, depending on the elements being studied. Their physical structure will be investigated by heating experiments in an analytical transmission electron microscope and then mapped onto the T-X-1/r 3-axis phase diagram. NON-TECHNICAL: Special attention will be given to the possibility of discovery of new phases in the nanoparticles. The impact of a successful program is to provide new ways of understanding phase diagrams of nanoparticles. Such understanding provides broad usefulness in a range of technologies including sintering, strengthening, solders, and energy storage.