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Vapor-Phase Synthesis and Assembly of Reactive Metal Nanoparticles for Energetic Applications
PANKAJ GHILDIYAL, Prithwish Biswas, Steven Herrera, Reza Abbaschian, Michael Zachariah, University of Maryland, College Park
Abstract Number: 521
Working Group: Nanoparticles and Materials Synthesis
Abstract
Nanoscale reactive metals such as Mg, Al, Fe, and Ni are emerging candidates for designing materials for plasmonics, hydrogen storage, and energetic composites. Assembly of their nanoparticles (NPs) into well-defined structures is also highly desirable due to their collective properties that are sensitive to size, structure, and organization of particles in such assemblies. Aerosol synthesis provides a scalable route to continuous production of high-purity nanoparticles and their assemblies by circumventing the need for stabilizing agents typically employed in colloidal approaches. Here, we present a vapor-phase synthesis approach – electromagnetic levitation and heating – based on controlled-evaporation of bulk reactive metals to not only generate NPs of reactive metals but also assemble them into different aggregate assemblies. Using this approach, we have generated highly reactive Mg NPs with tunable sizes from ~20-500 nm.
We have evaluated the size-dependent reactivity and energetic performance of the synthesized Mg NPs as a fuel for different nanoscale oxidizers. Through in-situ time-of-flight mass spectrometry coupled with ignition and constant-volume combustion-cell measurements, we demonstrate that the Mg-release, ignition temperatures, reactivity, and energy release rates of the energetic composites can be controlled by tuning Mg particle size. We also show that the magnetic field employed in this technique allows for on-the-fly, vapor-phase assembly of metal nanoparticles into aggregates with different fractal dimensions that exhibit distinct morphologies and porosities. This method, therefore, enables scalable synthesis and assembly of nanoscale metals, opening possibilities for large-scale manufacturing of materials with tunable reactive behavior as well as morphological and structural features.