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Aluminum Cluster-Based Materials for Propulsion and Other Applications and Catalysis
VIRGINIA COMMONWEALTH UNIV RICHMOND
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During the current project, we have identified classes of stable cluster motifs for implementation as building blocks of nanoenergetic materials and developed guiding principles for their synthesis. To begin, differing mechanisms that can stabilize clusters were identified. The first refers to crystal field like splitting of electronic shells via geometrical distortions that can lead to stable species at sub-shell fillings. Such a mechanism accounted for the stability of CuAl22- and more recently, CuMg8- and AuMg8- . It was shown that aromaticity, traditionally used to understand stability of organic systems, can also stabilize metallic clusters. Al3Bi was shown to be the first neutral all-metal aromatic species. Similar clusters containing As and Sn in place of Bi, are also stabilized by and delocalized orbitals. Nanoenergetic materials need to be air stable and hence studies on the reactivity of aluminum cluster anions with water were undertaken. Theoretical investigations showed that the reactivity proceeded through Lewis acidLewis base pair of complementary active sites that break OH bond and clusters with two pairs of such sites generated hydrogen. These findings also led to new class of nanocatalysts that can break polar covalent bonds and recent studies showed that such pairs can even break CO bonds. Finally, protocols that can enable synthesis of clusters assembled materials were formulated by focusing on cluster assemblies made from As11 and K that contain linear and helical chains.
APPROVED FOR PUBLIC RELEASE