68th International Symposium on Molecular Spectroscopy
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
Introduction and Motivation
From a cold hammer to a fireball: How does it happen?
Mechanical
Energy
Chemical
Energy
http://www.bbc.co.uk/news/science-environment-11485672
Mechanical Energy
(Shock, impact, friction)
Warm EM
Cold EM
Without
Energy Concentration
process
With
Energy Concentration
process
Hot Spot Generation
∆Hrxn > Hdissipation
Computed critical
conditions for hot
spot growth in HMX
and TATB
Growing hot spot
(causes detonation)
go
∆Hrxn < Hdissipation
Dying hot spot
(no rxn or gradual burning)
no go
Tarver, C. M.; Chidester, S. K.; Nichols, A. L., J. P. Chem., 100 , 5794 (1996).
MIR Camera
objective lenses
High-speed
MCT MIR
camera
Object
“Telescope orientation”
 Sensor type: mercury
cadmium telluride
(MCT, >90% quantum
efficiency)
PC
“Microscope orientation”
 Spectral response
range: 3.7-4.8 µm.
 Pixel pitch: 15 µm.
 Frame speed: up to
120fps.
Vis.
NIR
SWIR
MIR
LWIR
FIR
THz
λ(μm)= 0.39
0.75
1.4
3
8
15
100
1000
laser
500ms
Dichroic mirror
shutter
To camera
50ms
Salt window
Sample
Salt window
IMAQ
Periscope
Protection window
Beam dump
CO2 laser
driver
AOM
(diffraction not shown)
CO2 laser
PC
High-speed
MCT Mid-IR
camera
f/2.0 camera lenses
Pulse/delay generator
RDX (1,3,5-Trinitroperhydro1,3,5-triazine)
T(K)
νLaser = 974.6cm-1
50ms
100ms
300ms
400ms
500ms
1000ms
~500μm
2W
Gradual heating
20W
Decomposition temperature: ~440K
312K
300K
colder
warmer
313K
300K
Energy concentrated on the vertex edge.
310K
900
920
940
960
980
1000 1020 1040 1060 1080 1100
300K
~500μm
RDX FTIR spec.
900
920
940
960
980
1000 1020 1040 1060 1080 1100
frequency (cm-1)
Laser Photons Concentrate in
Crystal
Refractive index = 1.49 @ 10.6μm
ab 
D
θair


n
D  tan 180    tan    90  air sin 180  
nRDX







a β
θRDX b
θair
θRDX
I
 e   L
I0
Simulations
α(ω) = attenuation coeff.
L = path length
T(K)
~30THz Laser radiation
~30THz Laser radiation
313K
300K
100µm
500µm
α(ω)=1000cm-1
500µm
vs.
α=100cm-1
% of incident
photon flux
Summary and Future Works
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.
Acknowledgement
• Dr. Dana D. Dlott
• The Dlott research group
• Funding from the Office of Naval Research
THANKS FOR YOUR ATTENTION!!!
Ultrasonic Experiment
Sample holder
Ultrasonic horn
20 kHz, 750 W
13 mm tip size
Holder base
sample
with hole Sapphire
IR window
Four springs
connecting
holder and horn
Ultrasonic Energy Concentration:
wrapped
 Ultrasonic condition:
20% amplitude, 30 N cm-2
static pressure
W.
PEG-600 wrapped vs. naked NH4NO3
N.
1 mm
naked
Bkg
033
540 K
 Interfacial delamination
enhances the energy
concentration procedure in
the ultrasonic experiment.
→ Crystal-polymer surface
property is essential to the
hotspot generation.
05
523
W.
001
023
460 K
051
002
513
N.
013
052
003
380 K
053
004
503
1 mm
0.07 s
0.12 s
0.10 s
300 K
006
054
005
Oxidizer & Fuel: sucrose and KClO3, wrapped in one PEG-600 droplet
Before
Before
After
004
003
002
001
 Ultrasound can be used to
trigger the chemical reaction
of solid.
KClO3
sucrose
1 mm
Bkg
033
540 K
05
523
001
023
460 K
051
002
513
013
052
003
380 K
053
004
503
1 mm
0.07 s
0.08 s
0.09 s
300 K
006
054
005
004
003
002
001