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Coaxial Tungsten-Oxide/Aluminum Thermite Nanocomposite

Stephen Tse (Rutgers University), Zhizhong Dong (Rutgers University), Bernard Kear (Rutgers University), Jafar Al-Sharab (Rutgers University)

Prager Medal Symposium in honor of George Weng: Micromechanics, Composites and Multifunctional Materials

Mon 4:20 - 5:40

MacMillan 117

Al-coated tungsten-oxide nanowires, forming a thermite nanocomposite, are fabricated using a combined flame and solution synthesis method. Such geometry not only presents an avenue to tailor heat-release characteristics due to anisotropic arrangement of fuel and oxidizer, but also possibly eliminates or at least minimizes the presence of an Al2O3 passivation film between the aluminum and metal oxide. The tungsten-oxide nanowire array is fabricated using a counter-flow flame synthesis method. Specifically, vertically-well-aligned tungsten-oxide nanowires with diameters of 20-50 nm, lengths of 10-15 µm, and coverage density of 109-1010 cm-2 are grown on tungsten substrates at a gas-phase temperature ~1720 K. Subsequently, thin aluminum layers, with a thickness of ~16 nm, are deposited on the surface of the WO2.9 nanowires by an ionic-liquid electrodeposition method. The electrodeposition process does not obviously change the geometrical structure of the tungsten-oxide nanowires--only coating them. The composite nanowire has a coaxial structure, with outer diameter of 82.9 nm, inner diameter of 50.5 nm, and Al coating layer thickness of 16.2 nm, after 15 minutes of aluminum electrodeposition. HRTEM of the interfacial region between the outer Al layer and the tungsten-oxide core reveals that aluminum grows directly on the surface of tungsten-oxide nanowire. Analysis of the lattice planes of the core nanowire reveals an average spacing of 3.78 Å, which corresponds to the reflections from the {110} planes of WO2.9 tetragonal phase. The coating layer has a lattice plane spacing of 2.33 Å, which corresponds to the reflections from d-spacing of {111} planes of Al. To verify the reactivity of the as-synthesized thermite nanocomposite, a tungsten wire (used as substrate) with tungsten-oxide/aluminum coaxial nanowires on its surface is resistively heated, resulting in explosive combustion of the nanocomposite array.