Aluminum burn rate modifiers based on reactive nanocomposite powders

Aluminum powders have long been used as additives in propellants, pyrotechnics, and explosives. Aluminum has a high enthalpy of combustion but relatively low burn rate. Addition of reactive nanocomposite powders can increase the burn rate of aluminum and thus the overall reaction rate of the energetic formulation. Replacing only a small fraction of the fuel by a nanocomposite material can enhance the reaction rate with little change to the thermodynamic performance of the formulation. This research showed the feasibility of the above concept using nanocomposite powders prepared by arrested reactive milling (ARM), a scalable "top-down" technique for manufacturing reactive nanomaterials. The nanocomposite materials used in this study were 2BρTi, and Al-rich thermites: 8Alρ3CuO, and 8AlρMoO3. The reactive nanocomposite powders were added to micrometer-sized aluminum powder and the mixture was aerosolized and burned in a constant volume chamber. The combustion atmosphere was varied using oxygen, nitrogen, and methane. The resulting pressure traces were recorded and processed to compare different types and amounts of modifiers. Additives of nanocomposite powders of 8Al + MoO ₃ and 2B + Ti to micrometer- sized aluminum were found to be effective in increasing both the rate of pressure rise and maximum pressure in the respective constant volume explosion experiments. It was observed that 20 wt.-% of additive resulted in the best combination of the achieved burn rate and pressure.