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 MURI Program Review, October 16, 2003

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

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

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

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

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

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

Prototypical Lennard-Jones system t=0pst=0.1675pst=0.3350pst=0.5025pst=0.6700pst=0.8375ps (T* = 0.935,  = 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

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

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

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

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

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

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

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

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

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°

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