1 / 22

OLD GUARD TECHNICAL WEB PAGE COMPETITION

OLD GUARD TECHNICAL WEB PAGE COMPETITION. Prepared By: Ben Tsui, College of Staten Island Assisted by: Kushal Jain, College of Staten Island Combustion of Off-Stoichiometric Al-MoO3 Nano-composite Powders in Dry Air. Original research by: Soumitri S. Seshadri, Swati Umbrajkar,

cree
Download Presentation

OLD GUARD TECHNICAL WEB PAGE COMPETITION

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. OLD GUARD TECHNICAL WEB PAGE COMPETITION Prepared By: Ben Tsui, College of Staten Island Assisted by: Kushal Jain, College of Staten Island Combustion of Off-Stoichiometric Al-MoO3 Nano-composite Powders in Dry Air Original research by: Soumitri S. Seshadri, Swati Umbrajkar, Vern Hoffmann, and Edward L. Dreizin

  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 • Nanocomposite thermite: • A very rapid reaction • No free Al left to react with external oxidizer • AP in propellants • Air in thermobaric explosives • Metal-rich thermites: • Free Al remains • Find the minimum concentration of thermite oxidizer required to achieve the high reaction rates? ? This work: Fuel: Al; Oxidizer: MoO3

  4. Technical approach • Prepare a set nano-composite materials xAl+MoO3using 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. Time of Reaction For Reactive Milling Temperature of Milling Vial Milling Time 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. Al2O3 Mo Al MoO3 Epoxy Nanocomposite morphology: 4Al+MoO3 (A)

  7. Nanocomposite morphology: 4Al+MoO3 (B) Nano-scale network of reactive boundaries

  8. Nanocomposite morphology: 8Al+MoO3

  9. Phase analysis of nanocomposite powders XRD Analysis: undesirable partial reaction reducing MoO3 begins

  10. Particle size distributions Shows average size to be too large.

  11. Reducing particle sizes for 8Al+MoO3 Actual mixture used. • Wet milling found ineffective • Sifting used • Sifting performed under hexane in a glovebox to ensure safety Average size is too large. • Sifting reduces the volume fraction of larger particles to approximate reference size • The position of the size distribution mode changes only slightly

  12. Test Setup : Constant Volume Explosion • Constant volume explosion (9.2 liter explosion vessel) • Pressure tracesand 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 • CEA Code by Gordon and McBride (NASA), constant volume condition • For pure Al burning in air, Tmax occurs at an equivalence ratio of j= 1.02 • For 9.2 liter vessel filled with air at 1 atm, this corresponds to 2.89 g load of Al

  15. Fuel Load Matrix • Gas Composition: 22.5% O2 , 77.5% N2 • Mass loads of thermite mixtures are determined using their theoretical maximum densities and selecting the mass, for which the volume is equal to that of 2.89 g of pure Al i.e. constant volume. • The overall mass of available Al is smaller for thermite mixtures

  16. Pressure Traces Al 4Al+MoO3 8Al+MoO3 Estimated flame temperatures, K: 1780 1730 1350

  17. Pressure differentials (dP/dt)

  18. Discussion of Results • Flames produced by nanocomposite thermites propagate much faster than those produced by pure Al powder • Reaction pressure is highest for Al, closely followed by that for 8Al+MoO3 and followed by that for 4Al+MoO3 • The reaction pressures indicate that the flame temperatures are much lower than calculated adiabatic flame temperature • Despite larger size particles and smaller mass of Al available, the nanocomposite powder 8Al+MoO3 performed better than other materials • Equivalent heat of reaction is proportional to (Tflame-Troom)/mAl • the heat of reaction can be estimated as (mair+mfuel)Cp∙ DT/mAl

  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. • The reaction energies for Al and 8Al+MoO3 are nearly the same • The reaction rates for nanocomposite fuel-rich thermite powders are • much higher than that for Al

  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

  22. WELCOME TO THE COLLEGE OF STATEN ISLAND WE WOULD LIKE TO THANK YOU FOR VISITING OUR WEBSITE PLEASE MAKE YOUR CHOICE FROM THE FOLLOWING OPTIONS

More Related