1. University of Missouri-Columbia Department of Chemistry Energy Transfer at a Liquid Surface Towards a Prediction of the Steady-State Surface Temperature of a Burning Energetic Material John E. Adams, Tamas Szabo, Ali Siavosh-Haghighi Department of Chemistry University of Missouri-Columbia Columbia, MO 65211-7600 MURI Program Review, October 16, 2003

2. Context Early deflagration models –gasification + single reaction –no explicit chemical mechanisms Refined models –inclusion of one or more condensed-phase reactions –detailed gas-phase combustion chemistry –gas-phase transport –phenomenological treatment of the dependence of burning rate on T s MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

3. Goal of This Work Predict the burning rate from first principles (depends on surface temperature) –Evaporation –Gas-phase combustion –Liquid surface heating by hot combustion products –Condensed-phase reactions –Melting solid material as surface regresses MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

4. Previous Work Gas-liquid scattering—early work –Sinha and Fenn (1975) –Balooch, Siekhaus, and Olander (1986, 1988) Nathanson group –Scattering of inert gases and small molecules (CH 4, NH 3, D 2 O, SF 6 ) from liquids and solutions having low vapor pressures (glycerol, squalane, conc. H 2 SO 4, perfluorinated polyethers, metals, alloys) –TOF spectra, in-plane scattering flux as a function of incident and observation angles University of Missouri-Columbia Department of Chemistry MURI Program Review, October 16, 2003

5. Strategy Develop simulation code for energy transfer studies –DL_POLY_2 (v. 2.14) modules All degrees of freedom included Extensive set of included potential descriptions –Inclusion of impinging species (energy selected) –Energy analysis of scattered or trapped species MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

6. Strategy (continued) Investigate model system to test code, establish basic behavior –Lennard-Jones system –Generation of interface Equilibration of the liquid Expansion of the simulation cell –Surface-temperature dependence of energy transfer MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

7. Surface profile (LJ model) MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

8. Prototypical Lennard-Jones system t=0pst=0.1675pst=0.3350pst=0.5025pst=0.6700pst=0.8375ps (T* = 0.935,  = 5.04524 kJ/mol,  = 2.81 Å, E i = 92 kJ/mol;  i = 55°) MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

9. t=1.0050pst=1.1725pst=1.3400pst=1.5075pst=1.6750pst=1.8425ps MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

10. t=2.0100pst=2.1175pst=2.3450pst=2.5125pst=2.6800pst=2.8475ps MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

11. t=3.0150pst=3.1825pst=3.3500pst=4.0200ps E f = 82.1 kJ/mol,  f = 70.5° (70.2° in plane of incidence) MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

12. Energy Transfer (“low T”) MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

13. Energy Transfer (“high T”) MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

14. Nitromethane Simple energetic material, prototype for CHNO explosives Full potential description from Agrawal, Rice, and Thompson –Good structural parameters –Good melting temperature MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

15. T = 360 K, P = 1 bar T = 0 K MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

16. Density Contour MURI Program Review, October 16, 2003 University of Missouri-Columbia Department of Chemistry

17. University of Missouri-Columbia Department of Chemistry MURI Program Review, October 16, 2003 Energy Transfer E i = 8.31 kJ/mol  i = 55° E f = 2.97 kJ/mol  f = 47°

18. To Do... Complete nitromethane study –Variety of impinging species (mass, internal degrees of freedom, reactivity) –Energy transfer as a function of surface temperature –Need typical surface fluxes, energies* Begin study of model system for which gas- phase combustion kinetics is known