OLD GUARD TECHNICAL WEB PAGE COMPETITION

1. OLD GUARD TECHNICAL WEB PAGE COMPETITION

2. ABSTRACT Aluminum as a fuel Advantages High oxidation enthalpy High combustion temperature Environmentally benign products Problems Ignition delay leading to agglomeration of molten particles Low bulk burn rates, incomplete combustion Approach Enable rapid ignition assisted by thermite reaction: Al+MoO3? Al2O3+Mo Use nanocomposite powders to achieve high reaction rate Determine the minimum concentration of MoO3 necessary for rapid and complete combustion of aluminum with external oxidizer Target applications: metallized propellants, thermobaric explosives

3. Proposed Concept

4. Technical approach Prepare a set nano-composite materials xAl+MoO3 using Arrested Reactive Milling (ARM), with x > 4 (stoichiometric x=2) Characterize prepared powders Particle size distributions; low angle laser light scattering, Coulter LS 230 Particle composition, morphology: XRD, SEM Carry out equilibrium thermodynamic calculations for combustion of the prepared materials in air Determine optimum metallic fuel loads for the constant volume explosion experiments Use NASA CEA code Perform constant volume explosion experiments to assess the reaction rate and completeness for different materials Use results for spherical Al powders as a baseline

5. Arrested Reactive Milling Starting components: powders of Al and MoO3 Process Mill with steel balls to prepare nanocomposite powder Use hexane as a process control agent Stop milling before the thermite reaction is mechanically triggered Product: micron-sized nanocomposite powders

6. Nanocomposite morphology: 4Al+MoO3 (A)

7. Nanocomposite morphology: 4Al+MoO3 (B)

8. Nanocomposite morphology: 8Al+MoO3

9. Phase analysis of nanocomposite powders

10. Particle size distributions

11. Reducing particle sizes for 8Al+MoO3

12. Test Setup : Constant Volume Explosion Constant volume explosion (9.2 liter explosion vessel) Pressure traces and ignition pulse recorded with digital oscilloscope

13. Selecting experimental conditions Use comparable particle sizes Fuel load selected to enable the maximum flame temperature at given initial pressure (1 atm) selected based on the vessel pressure rating Mass of Al determined based on thermodynamic equilibrium calculations Mass of Al-MoO3 powders selected to ensure the constant fuel volume (equal to that of pure Al) to produce legitimate comparisons of the reaction rates and energies

14. Thermodynamic Calculations

15. Fuel Load Matrix

16. Pressure Traces

17. Pressure differentials (dP/dt)

18. Discussion of Results

19. Conclusions Powders of aluminum-rich thermites with MoO3 as an oxidizer are produced by Arrested Reactive Milling Produced powders comprise micron-sized, pore-free particles Each particle is a nanocomposite of Al and MoO3 Powder size distributions measured using low-angle laser light scattering Any coarser powder is sieved to approach the size distribution of pure Al powder used as the reference Constant volume explosion experiments used to compare reaction rates and energies of different materials Air is used as an oxidizer Fuel load for Al is selected based on thermodynamic calculations showing the maximum adiabatic flame temperature Fuel loads for nanocomposite powders selected to match the volume of solid fuel for Al

20. Applicability Due to these higher reaction efficiencies, nanocomposite thermites prove to be effective components for propellants, thermobaric explosives and pyrotechnics. This will result in safer, more reliable and higher efficiency products.

21. Additional Research Effects of even higher concentrations of Molybdenum Oxide will be investigated Reaction completeness will be determined by analysis of collected combustion products Ignition kinetics for metal-rich thermites will be quantified by thermal analysis and additional experiments Additional thermite compositions (e.g., using CuO as an oxidizer) will be studied