Aluminum-Rich Al-MoO3 Nanocomposite Powders Prepared by Arrested Reactive Milling

Abstract

Fuel-rich Al-MoO 3 nanocomposites were prepared using arrested reactive milling. Powder composition was varied from 4Al + MoO 3 to 16Al + MoO 3 . Powders were evaluated using electron microscopy, thermal analysis, x-ray diffraction, heated-filament-ignition experiments, and constant-volume-explosion experiments. Uniform mixing of MoO 3 nanodomains in the aluminum matrix was achieved for all prepared powders. Multiple and overlapping exothermic processes were observed to start when the nanocomposite powders were heated to only about 350 K. In heated-filament experiments, all nanocomposite powders ignited at temperatures well below the aluminum melting point. Ignition temperatures for these powders were estimated for the higher heating rates that are typical of fuel-air explosions. Constant-volume-explosion experiments indicated that flame propagation in aerosols of nanocomposite thermite powders in air is much faster than that in pure aluminum aerosols. The energy release, normalized per unit mass of aluminum, was higher for the nanocomposite materials with bulk compositions 4Al + MoO 3 and 8Al + MoO 3 and lower for pure aluminum and for the 16Al + MoO 3 nanocomposite sample. The reaction rate was the highest for the 8Al + MoO 3 nanocomposite powder. The combustion efficiency inferred from the measured pressure traces correlated well with the phase compositions of the analyzed condensed combustion products.