Tuning energetic material reactivity using surface functionalization of aluminum fuels

Combustion analysis of three different thermites consisting of aluminum (Al) particles with and without surface functionalization combined with molybdenum trioxide (MoO₃) was performed to study the effect of surface functionalization on flame propagation velocity (FPV). Two types of Al particles had self-assembled monolayers (SAMs) of perfluoro tetradecanoic (PFTD) and perfluoro sebacic (PFS) acids around the alumina shell, respectively; the other one did not. Flame speeds for Al with PFTD acid combined with MoO ₃ are 86% higher than Al/MoO₃ whereas those for Al with PFS acid combined with MoO₃ are almost half of Al/MoO₃. The Al-PFTD structure is more sterically hindered and exhibits lower bond dissociation energy. This chemistry promotes increased flame speeds. Thermal equilibrium studies were performed using a differential scanning calorimeter and a thermogravimetric analyzer to determine activation energy (E_a) of the thermites. Results are consistent with flame speed observations and showed an inverse relationship between flame speed and E_a. This study shows that surface functionalization can be used as an approach to control the reactivity of Al particles.