Dynamical effects of the oxide layer in aluminum nanoenergetic materials

Dynamical effects of the aluminum nanopowder oxide layer are investigated in nanoenergetic materials consisting of nitrocellulose (NC) oxidizer containing embedded similar to 60 nm diameter Al having thinner (2.5 nm) or thicker (6 nm) oxide layers. Following laser flash-heating, a hot spot is formed near each Al particle. The mean distance of reaction propagation d(rxn) from the hot spot through the nitrocellulose is determined with similar to 100 nm resolution. With 100 ps pulses a shock propagation mechanism is dominant, and with 10 - 25 ns pulses reaction a thermal explosion mechanism is dominant. When higher energy picosecond pulses are used, d(rxn) is observed to be significantly increased with thicker oxide layers, but using nanosecond,pulses d(rxn) is slightly decreased with thicker oxide layers. Ibis oxide layer enhancement of d(rxn) with picosecond pulses is attributed to the thicker oxide layer confining the hot Al for several tens of picoseconds, resulting in a larger shock wave. This work supports the view of the oxide layer as deadweight for slower heating rate processes such as combustion, but it suggests a thicker oxide layer may be of some benefit for extremely high heating rate processes involved in detonation or high speed deflagration of nanoenergetic materials.