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This work investigates the reaction mechanism of metastable intermolecular composites by collecting simultaneous pressure and optical signals during combustion in a constant-volume pressure cell. Nanoaluminum and three different oxidizers are studied: CuO, SnO 2 , and Fe 2 O 3 . In addition, these mixtures are blended with varying amounts of WO 3 as a means to perturb the gas release in the system. The mixtures with CuO and SnO 2 exhibit pressure signals that peak on timescales faster than the optical signal, whereas the mixtures containing Fe 2 O 3 do not show this behavior. The burn time is found to be relatively constant for both CuO and SnO 2 , even when a large amount of WO 3 is added. For Fe 2 O 3 , the burn time decreases as WO 3 is added, and the temperature increases. The results are consistent with the idea that oxidizers such as CuO and SnO 2 decompose and release gaseous oxidizers fast, relative to the burning, and this is experimentally seen by an initial pressure rise followed by a prolonged optical emission. In this case, the burning is rate limited by the aluminum, and it is speculated to be similar to the burning of aluminum in a pressurized oxygenated environment. For the Fe 2 O 3 system, the pressure and optical signals occur concurrently, indicating that the oxidizer decomposition is the rate-limiting step.

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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 (∼105 K/s) platinum wire. Ramping the wire temperature 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.