Diffusive vs Explosive Reaction at the Nanoscale

Solid-solid reactions at the nanoscale between a metal passivated with a nascent oxide and another metal oxide can result in a very violent reaction. This begs the question as to what mechanism is responsible for such a rapid reaction. The ignition of nanoscale Al/CuO thermites with different aluminum oxide shell thicknesses were investigated on a fast heated (similar to 10(5) K/s) platinum wire. Ramping the wire temperature to similar to 1250 K and then shutting off the voltage pulse result in ignition well after the pulse is turned off; i.e., an ignition delay is observed. The delay is used as a probe to extract the effective diffusion coefficient of the diffusing species, which is confirmed by fast time-resolved mass spectrometry. The results of this study are consistent with a diffusion controlled ignition mechanism.