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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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

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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).

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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

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• 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

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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

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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.)

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• 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

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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%)

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Double pulse spectra (argon)Double pulse spectra (argon)

Al

Cu

Ni

Sn

Ti

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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

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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

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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

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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

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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

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Aluminum powder additiveAluminum powder additive

• increasing the Al:↑ T– ↑ Texc

– ↓ substrate emission– ↑ Al emission

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– ↑ AlO emission

Aluminum powder additiveAluminum powder additive

• increasing the Al:– ↓ C, H, N, O and CN emission (less RDX sampled?)

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– ↑ 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

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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

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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