Metallic fuels are attractive alternatives to organic fuels in energetic materials, due to their higher energy densities and favorable mechanical properties. However, so far the addition of reactive metals into explosive systems has had limited application, primarily because of the relatively slow rate of energy release. It has been proposed that to overcome this limitation, the domain sizes of the fuel be reduced to the nanoscale, where the kinetics may reasonably be expected to approach those of conventional molecular explosives. Investigations of such nanometric metal fuel particles have been limited to a small number of systems and are complicated because oxidation at the surface of the fuel particles is difficult to avoid. At the smallest domain sizes, where the kinetics should be most favorable, the oxide layer at the surface of the metal fuel particles makes up a significant portion of the total volume, thereby introducing unacceptable amounts of inert material. Recent promising experiments have revealed that certain compositions and morphologies of nanometric clusters (e.g., Al13-) are preferentially resistant to unintentional oxidation. A new research program underway at AFRL/MN aims to use modern cluster beam deposition techniques to search through a wide range of nanocluster compositions and morphologies-quickly-and to produce sufficient quantities of material to evaluate their macroscopic energetics and stability. Nanoclusters produced by laser vaporization, buffer-gas condensation and/or supersonic expansion in vacuum will be formed into a beam and soft-landed onto a substrate. Varieties of pure and mixed clusters will be explored and include novel metal/metal-oxide core-shell nanoclusters as a means of improving the intimate contact between the oxidizer and fuel. The composition, morphology, and reactivity of these nanoclusters will be probed before and after deposition using conventional spectroscopies, mass-spectrometry, calorimetry, and surface science methods.

 

key words

Nanoclusters; Thermites; Core-shell particle; Rare gas clusters; Spectroscopy; Soft-landing; Deposition; Thin film; UHV; Surface science;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral and Senior applicants