1. Hot Spot Generation in Energetic Materials by Applying Weak Energies Ming-Wei Chen, Sizhu You, Kenneth K. Suslick and Dana D. Dlott 6/18/2012 68 th International Symposium on Molecular Spectroscopy

2. From a cold hammer to a fireball: How does it happen? Cold EM Mechanical Energy (Shock, impact, friction) Warm EM Without Energy Concentration process No detonation With Energy Concentration process Exothermic process Local heating http://www.bbc.co.uk/news/science-environment-11485672 Mechanical Energy Chemical Energy

3. ∆H rxn > H dissipation Growing hot spot (causes detonation) ∆H rxn < H dissipation Dying hot spot (no rxn or gradual burning) Computed critical conditions for hot spot growth in HMX and TATB go no go Tarver, C. M.; Chidester, S. K.; Nichols, A. L., J. P. Chem., 100, 5794 (1996).

4.  Sensor type: mercury cadmium telluride (MCT, >90% quantum efficiency)  Spectral response range: 3.7-4.8 µm.  Pixel pitch: 15 µm.  Frame speed: up to 120fps. NIRSWIRMIRLWIRFIR THz Vis. λ(μm)=0.39 0.751.4 3 8 151000 100 “Telescope orientation”“Microscope orientation” High-speed MCT MIR camera objective lenses Object PC

5. High-speed MCT Mid-IR camera f/2.0 camera lenses PC CO 2 laser CO 2 laser driver Pulse/delay generator AOM (diffraction not shown) Periscope shutter IMAQ 500ms 50ms To camera Dichroic mirror Salt window Sample Protection window laser Beam dump

6. 50ms300ms400ms500ms1000ms100ms T(K) 2W 20W ν Laser = 974.6cm -1 ~500 μ m Decomposition temperature: ~440K Gradual heating

7. ~500 μ m 300K 312K 300K 313K 300K 310K colderwarmer Energy concentrated on the vertex edge. RDX FTIR spec.

8. Refractive index = 1.49 @ 10.6μm

9. ~30THz Laser radiation 100µm 500µm % of incident photon flux α(ω) = attenuation coeff. L = path length 300K 313K T(K)

10.  Summary:  A thermal/MIR imaging microscope apparatus has been built, and can be used in the laser and ultrasound experiments.  Under laser exposure, the hotspot was found due to the concentrated laser photons in crystal. The thermal emission is related to the laser photon flux.  Future works:  Complete the theory to interpret the observation in laser experiment.  Clarify the mechanisms of energy concentration.  Extend the application of apparatus for studying different materials.

11. Dr. Dana D. Dlott The Dlott research group Funding from the Office of Naval Research THANKS FOR YOUR ATTENTION!!!

13. Ultrasonic horn 20 kHz, 750 W 13 mm tip size Sample holder Holder base with hole Sapphire IR window sample Four springs connecting holder and horn

14. 0.07 s 0.10 s 0.12 s Bkg 540 K 300 K 380 K 460 K PEG-600 wrapped vs. naked NH 4 NO 3 W. N. wrapped naked W. N. Oxidizer & Fuel: sucrose and KClO 3, wrapped in one PEG-600 droplet KClO 3 sucrose Before After 540 K 300 K 380 K 460 K 0.07 s 0.08 s 0.09 s Bkg 1 mm  Ultrasonic condition: 20% amplitude, 30 N cm -2 static pressure  Interfacial delamination enhances the energy concentration procedure in the ultrasonic experiment. → Crystal-polymer surface property is essential to the hotspot generation.  Ultrasound can be used to trigger the chemical reaction of solid.

15.  Mostly studied by theoretical works.  Aims: Real time, spatial resolved IR imaging experiments with sufficient time resolution.  Mechanism and dynamics of hot spot generation.  Control the chemical reaction. Computed critical conditions for hot spot growth in HMX and TATB go no go Tarver, C. M.; Chidester, S. K.; Nichols, A. L., J. P. Chem., 100, 5794 (1996).

16. Fit with estane data: Temp. = a * (ratio) b + c High-speed MCT MIR camera f/2.0 objective lenses thermocouple Temp. ctrl. & read heater Estane or gold film on substrate estane Black body radiation curve under-estimates the temperature in higher temperature region est.

17. E. C. Mattos, E. D. Moreira, R. C. L. Duttra, M. F. Diniz, A. P. Riberiro, K. Iha, Quim. Nova, 27, 540-544 (2004) RDX Type II Class 1 Decomposition temperature: ~440K Melting temperature: ~460K

18. RDX/KBr pellet RDX powder film CO 2 laser lines Decomposition temperature: ~440K

19. 946.0949.5970.5973.3979.7983.3 ~500 μ m 300K 312K 300K 313K 300K 310K ν Laser = colderwarmer Energy concentrated on the vertex edge.

20. ~30THz Laser radiation 100µm 500µm % of incident photon flux α = attenuation coeff. L = path length

21.  Simulation of intensity viewed by camera after correction with solid angle change in deeper layer.  Diffusion of hot spot is not considered in simulation.