(394h) Combustion of off-Stoichiometric AlMoO3 Nano Composite Powders in Dry Air

Fully dense, nano-composite Al-MoO₃ powders with excess Al were prepared by Arrested Reactive Milling (ARM) as potential components for propellants, explosives, and pyrotechnics. The thermite reaction reducing MoO₃ is expected to boost the Al ignition rate. It is desired to determine the minimum concentration of MoO₃ that enables rapid and complete combustion of aluminum. In the first part of this investigation, nanocomposite powders with the bulk composition 4AlMoO₃ and 8AlMoO₃ were produced and their combustion was compared to that of pure aluminum powder in air. The combustion experiments were conducted in a 9.2 L closed vessel. The mass load of aluminum powder was determined from thermodynamic calculations to ensure the maximum flame temperature. To maintain consistency in the experiment, the amount of the nano-composite powder loaded in the vessel was selected to match the volume of the pure Al load. Specifically, 2.89 g, 3.81 g and 3.48 g of Al, 4AlMoO₃ and 8AlMoO₃ respectively, were aerosolized in the explosion vessel and ignited at its center using a heated wire while monitoring the vessel pressure in real time as the flame propagated outward. The results showed that both the pressure increase and rate of pressure rise produced in the vessel by combustion of the AlMoO₃ mixture is greater than that of Al. Furthermore, the mixture with the lesser concentration of MoO₃ performed better than the mixture with a greater concentration of MoO₃. The project will continue with producing and testing nanocomposite powders with increasingly greater concentrations of Al to establish the minimum concentration of MoO₃ needed to achieve rapid and complete combustion. A special care is taken to ensure the similarity of the particle size distributions for different powders used in the constant volume explosion tests.