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U.S. Army Research, Development and Engineering Command
Laser-induced plasma chemistry of the explosive RDX with various metals
Laser-induced plasma chemistry of the explosive RDX with various metals
Jennifer L. GottfriedU.S. Army Research Laboratory (WMRD)
Aberdeen Proving Ground MD
Jennifer L. GottfriedU.S. Army Research Laboratory (WMRD)
Aberdeen Proving Ground MDAberdeen Proving Ground, MDAberdeen Proving Ground, MD
Presented at: NASLIBS 201118 July 2011Clearwater Beach FLClearwater Beach, FL
UNCLASSIFIED
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1. REPORT DATE 18 JUL 2011 2. REPORT TYPE
3. DATES COVERED 00-00-2011 to 00-00-2011
4. TITLE AND SUBTITLE Laser-induced plasma chemistry of the explosive RDX with various metals
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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18
OutlineOutline
Motivation Understand chemistry between metal nanoparticles and molecular explosives
Develop more efficient explosives
LIBS Nanoparticle production followed by laser-induced plasma chemistry
Time-resolved emission spectra
Laser Parameters Laser pulse energy dependence Single vs. double
pulse
Substrate characterization Matrix effects Effect of impurities on
chemistry
Experiments Double pulse (air/argon) Aluminum powder additives
RDX
UNCLASSIFIED
RDX discrimination RDX residue on various metals Effects of substrate on
discrimination
MotivationMotivation
Investigated formation of carbon in aluminized-RDX shock tube initiation
• XRD confirmed presence of C and Al2O3 in blast residue
Production of AlO and C decreases rocket propellant performance
• AlO and C2 emission collected with two 2-nm resolution monochrometers/PMTs
Observed that ↑ micron-Al results in ↑ C2 emission
UNCLASSIFIED
Our idea was to use Al nanoparticles rather than conventional micron-sized Al and look at the emission from additional atomic and molecular species, all on a much smaller scale
MethodologyMethodology
• In the past decade, laser ablation has increasingly been used to produce metallic nanoparticles– the size and distribution of the
nanoparticles can be controlled by:• sequential laser pulses, varying
repetition rates• laser fluence, wavelength and
pulse width• carrier gas (air, argon, nitrogen,
etc.)
J. Laser Micro. Nanoengineer., 3(2), 100-105 (2008).
UNCLASSIFIED
MethodologyMethodology
Little or no sample preparation is needed
Key advantages of LIBS over the technique used by Song et al.:
• no need to cast explosive formulations• any type of material can be ablated with the laser as long as the laser energy >
breakdown threshold
Little or no sample preparation is needed
• laser-generated nanoparticle formation
The properties of the laser (pulse energy, wavelength, pulse duration) can be tuned to control the size of the particles formed
• no shock tube needed
The intermediate chemical reactions of RDX and Al can be studied on a smaller scale
• C + C → C2
Ability to track relative concentrations of a large number of atomic and molecular species simultaneously
UNCLASSIFIED
• C + O2 → CO + O, CO + O → CO2, Al + CO2 → AlO + CO• also H, N, CN
Laser pulse energy studiesLaser pulse energy studies
45
50 AlAl+RDX
35
40
25
30
O in
tens
ity
15
20AlO
5
10
UNCLASSIFIED
0210mJ 420mJ 210-210mJ 420-420mJ
Laser pulse energy studiesLaser pulse energy studies
2500
3000AlAl+RDX
2000
2500
1500
inte
nsity
1000
O
500
UNCLASSIFIED
0210mJ 420mJ 210-210mJ 420-420mJ
Survey of SubstratesSurvey of Substrates
Question: do trace impurities in the metal substrate affect the plasma chemistry?
Spectra of 68 metal substrates were acquired
• high-purity aluminum (99 999%) copper (99 999%) nickel
Samples surveyed included:
high purity aluminum (99.999%), copper (99.999%), nickel (99.98%), tin (99.998%) and titanium (99.998%)
• numerous metal alloys including brass, lead and steel
Differences in the spectra were observed based on trace element additives and impurities
UNCLASSIFIED
Aluminum AlloysAluminum Alloys
• Alumina (Al2O3)
• NIST 1256b (82.99%)– 9.362% Si (obs.), 3.478% Cu
(obs.), 1.011% Zn (obs.)– <1% Fe, Mn, Ni, Sn, Sr, Ti (obs.)– <0.1% Cr, Mg, Pb, V (not obs.)0.1% Cr, Mg, Pb, V (not obs.)
• NIST 1259 (89.76%)– 5.44% Zn (obs.), 2.48% Mg
(obs.), 1.60% Cu (obs.), 0.025% Be (obs )Be (obs.)
– <0.2% Cr, Fe, Mn, Ni, Si (not obs.)
• NIST 1715 (94.58%)4 474% M ( b ) 0 3753% M– 4.474% Mg (obs.), 0.3753% Mn (obs.)
– <0.1% Cr, Cu, Fe, Ni, Pb, Si, Sr, Ti, V, Zn (not obs.)
UNCLASSIFIED
• Aluminum (99.999%)
Aluminum – C signalAluminum – C signal
1 2
1.4
Blank
1
1.2 BlankBlank+RDX
0 6
0.8
C/A
r
0.4
0.6
0.2
UNCLASSIFIED
0Al Al1715 Al1259 Al1256b Alumina
Aluminum – AlO signalAluminum – AlO signal
0 25
0.3
Blank
0.2
0.25 Blank+RDX
0.15
AlO
/Ar
Impurities make a huge difference in chemistry!
0.1
A y
0
0.05
UNCLASSIFIED
0Al Al1715 Al1259 Al1256b Alumina
Double pulse experimentsDouble pulse experiments
Double-pulse spectra acquired using a Continuum Surelite two-laser system w/echelle spectrograph (EMU-65 with an EMCCD camera)
• 420 mJ per laser, Δt=2μs, tdelay=1.0μs, tgate=50μs
Spectra of 5 substrates with and without RDX residue were obtained in air and under an argon flow
• Al (99.999%), Cu (99.999%), Ni (99.98%), Sn (99.998%), and Ti (99.7%)
UNCLASSIFIED
Double pulse spectra (argon)Double pulse spectra (argon)
Al
Cu
Ni
Sn
Ti
UNCLASSIFIED
1200 ~ c
:~~j . ! . ..-.
1200 800 400
::J 0 ____,.,......._~~---............ cri 1200 ._..., ~ 800 :t:
~ 400 2 0 E 1200
800 400
0 ---'--"'~------
1200 800 400
0
248.0
4000 H 3000 2000 1000
0 4000 3000 2000 1000
0 4000 3000 2000 1000
0
4000~ 3000 ~ 2000 1000
0 ~~-----~~-
4000 3000 2000 1000
0----,...,...,....,....,....,.....,...,~l""""r""',....,....,...,...,...,....,...,
249.0 652 654 656 658 660 662 Wavelength {nm)
TECHNOLOGY DRIVEN. WARFIGHTER FOCUSED.
Double pulse spectra (argon)Double pulse spectra (argon)
AlV.I. Babushok, F.C. DeLucia, P.J. Dagdigian, J.L. Gottfried et al., Kinetic modeling study of the laser-induced plasma plume of
l t i th l t i it i (RDX)
Cu
cyclotrimethylenetrinitramine (RDX), Spectrochim. Acta, Part B, 62B, 1321-1328 (2007).
Ni• the nitrogen must come from the explosive when under argon
Sn• therefore the CN formation is indicative of the chemical reactions the RDX undergoes in the plasma
TiC+N2 → CN+N
C2+N2 → 2 CN
p
UNCLASSIFIED
C2 N2 2 CN
Double pulse results (argon)Double pulse results (argon)
C+N2 → CN+N 0.06
C2+N2 → 2 CNCN Intensity0.05
0 02
C+N+M → CN+M
N In
tens
ity
0.04
0.02 0.04 0.06 0.08 0.10
0 02
0.03 0.18
0 4 0 6 0 8 1 0 1 2 1 4
0.02
UNCLASSIFIED
C Intensity
0.4 0.6 0.8 1.0 1.2 1.4
Double pulse results (argon)Double pulse results (argon)
C+O+M → CO+M0.06
C+O+M → CO+M
C+O2 → CO+O O Intensity0.050.0 0 5
CO+O → CO2
N In
tens
ity
0.04
0.5 1.0 1.5 2.0 4.0
0 02
0.03
0 4 0 6 0 8 1 0 1 2 1 4
0.02
UNCLASSIFIED
C Intensity
0.4 0.6 0.8 1.0 1.2 1.4
Double pulse results (argon)Double pulse results (argon)
CN+O → CO+N 0.12CN+O → CO+N
O Intensity0.10C
N In
tens
ity
0.08-4 -2 0 2 4
0.04
0.064 12
0 02 0 03 0 04 0 05 0 06
0.02
UNCLASSIFIED
N Intensity
0.02 0.03 0.04 0.05 0.06
Aluminum powder additiveAluminum powder additive
<75 μm Al powder mixed with RDX in varying
• 1:0, 1:1, 1:2, and 1:4 RDX to Al mixtures• substrates: Al, Cu, Ni, Sn, and Ti
<75 μm Al powder mixed with RDX in varying concentrations
, , , ,• double pulse laser system under argon
RDX/Al i t h d t th b t t
• each laser shot would blow off a significant amount of material• 15 spectra of each sample were acquired
RDX/Al mixtures were crushed onto the substrate surfaces
• 15 spectra of each sample were acquired
UNCLASSIFIED
Aluminum powder additiveAluminum powder additive
• increasing the Al:↑ T– ↑ Texc
– ↓ substrate emission– ↑ Al emission
UNCLASSIFIED
– ↑ AlO emission
Aluminum powder additiveAluminum powder additive
• increasing the Al:– ↓ C, H, N, O and CN emission (less RDX sampled?)
UNCLASSIFIED
– ↑ C2 emission (O being scavenged by the Al, less CO and CO2)
Aluminum powder additiveAluminum powder additive
• same optical emission trends observed on all 5 substrates• same optical emission trends observed on all 5 substrates (Al, Cu, Ni, Sn, and Ti)
• ↑ C2 and AlO confirms observations of Song et al !
UNCLASSIFIED
↑ C2 and AlO confirms observations of Song et al.!– decrease in atomic C is new information
Classification of RDX on metalsClassification of RDX on metals
PLS-DA model: 11 classes of pure metals with and without RDX
• RDX+(Al, Cu, Ni, Sn, Ti, Au, Mg, Zn, In, Ag) = 1 class• Al, Cu, Ni, Sn, Ti, Au, Mg, Zn, In, Ag• 20 latent variables
Test samples: additional spectra from each sample type
• 400 spectra in test set
• 160 spectra in aluminum alloy test set
Test samples: spectra acquired on metal alloys not in model
UNCLASSIFIED
p y• 280 spectra in other metal alloy test set
Classification of RDX on metalsClassification of RDX on metals
RDX Ag Al Au Cu In Mg Ni Sn Ti ZnAl+RDX (35) 34 0 5 0 0 0 0 0 0 0 0C +RDX (35) 35 0 0 0 1 0 0 0 0 0 0
92.5% true positives, 2.5% false positives
Cu+RDX (35) 35 0 0 0 1 0 0 0 0 0 0Ni+RDX (35) 28 0 0 0 0 0 0 33 0 0 0Sn+RDX (35) 31 0 0 1 0 0 3 0 0 0 0Ti+RDX (35) 35 0 0 0 0 0 0 4 0 1 0Au+RDX (5) 4 0 0 3 0 0 0 0 0 0 0Au+RDX (5) 4 0 0 3 0 0 0 0 0 0 0Mg+RDX (5) 5 0 0 0 0 0 4 0 0 0 0Zn+RDX (5) 5 0 0 0 0 0 0 0 0 0 1Ag+RDX (5) 5 0 0 0 0 0 0 0 0 0 0In+RDX (5) 3 0 0 0 0 3 0 0 0 0 0In RDX (5) 3 0 0 0 0 3 0 0 0 0 0Ag (5) 0 5 0 0 0 0 0 0 0 0 0Al (35) 0 0 35 0 0 0 0 0 0 0 0Au (5) 0 0 0 5 0 0 0 0 0 0 0Cu (35) 0 0 0 0 35 0 0 0 0 0 0( )In (5) 2 0 0 0 0 4 0 0 0 0 0Mg (5) 1 0 0 0 0 0 5 0 0 0 0Ni (35) 2 0 0 0 0 0 0 34 0 0 0Sn (35) 0 1 0 0 0 0 0 0 35 0 0
UNCLASSIFIED
Ti (35) 0 0 0 0 0 0 0 0 0 35 0Zn (5) 0 0 0 0 0 0 0 0 0 0 5
Classification of RDX on metalsClassification of RDX on metals
Classification of RDX dependent on substrate
emission lines
UNCLASSIFIED
Classification of RDX on Al alloys(not in model)
Classification of RDX on Al alloys(not in model)
UNCLASSIFIED
-0.5
-1.0
,...---------------------., o Alumina (AI120 3)
AI alloy 1256 AI alloy 1259 AI. alloy 1715
20 40
e A120 3 + RDX
Al1256 + RDX Al1259 + RDX Al1715 + RDX
60 80
0 0
100
• ••
• •
120 140 160 Test Sample#
TECHNOLOGY DRIVEN. WARFIGHTER FOCUSED.
Classification of RDX on otheralloys (not in model)
Classification of RDX on otheralloys (not in model)
UNCLASSIFIED
1.5
-1.0
50
0 0 <>
0
100 150 Test Sample #
~ <1 <1<J
rx1 Lead C2417 ead C2418
b. NiCu C 1248 ste,el1761
- steel C 1296 <l Ti 641 o Zn 625
Lead C2417 + RDX ead C2418 + RDX
NiCu C1248 + RDX steel 1761 + RDX steel C1296 + RDX Ti 641 + RDX
e Zn 625 + RDX
TECHNOLOGY DRIVEN. WARFIGHTER FOCUSED.
ConclusionsConclusions
Time-resolved, broadband emission of chemical species involved in the reaction of RDX and Al were observed
• plasma chemistry vs. shock tube detonationConfirmed observations of Song et al. using the new experimental methodologyexperimental methodology
• trace metals do affect chemistry, so broadband emission detection is extremely important
Compared pure metal vs. alloys emission detection is extremely importantalloys
• related to size of laser ablated particlesDemonstrated that laser
pulse energy affects pp gychemistry
Despite differences in the plasma chemistry, RDX residue on different metal
UNCLASSIFIED
p p ysubstrates can be correctly classified with PLS-DA