Michael R. Zachariah - UMD

Center for Energetic Concepts Development

U N I V E R S I T Y O F M A R Y L A N D, C O L L E G E P A R K, M D 2 0 7 4 2, U S A

T E L. 3 0 1 – 4 0 5 – 5 2 0 5 ; F A X 3 0 1 – 3 1 4 – 9 4 7 7 ; w w w . c e c d . u m d . e d u

Michael R. ZachariahProfessor

Probing the Reaction Dynamics of Nanoenergetic Materials

Department of Chemistry and Biochemistry




NanoEnergetic Materials

METAL/OXIDIZER

∆Hvolume (kcal/cc)

10 2 3

10 2 3 4 5 6 7

∆Hmass (kcal/g)

4

∆Hvolume

HIGH EXPLOSIVE

CL-20

TNT

PETN

HMX

Al/Ni2O3

Al/MoO3

Al/Teflon

Al/KClO4

∆Hmass

METAL/OXIDIZER

∆Hvolume (kcal/cc)

10 2 3

10 2 3 4 5 6 7

∆Hmass (kcal/g)

4

∆Hvolume

HIGH EXPLOSIVE

CL-20

TNT

PETN

HMX

Al/Ni2O3

Al/MoO3

Al/Teflon

Al/KClO4

∆Hmass

Fischer and Grubelich, 32nd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Lake Buena Vista, FL 1996. Thomas N. Hall and James R. Holden, Navy Explosives Handbook, NSWCMP 88-116, 1988.

2 32Al + 3MO Al O 3M H→ + ∆

Fuel Oxidizer

+




Energy release from Thermite > CHNO chemistry.

But, we know very little about mechanisms of ignition and propagation.

We are still groping to establish a conceptual mechanism, let alone advance to a mathematical model.

Thermodynamics

KineticsThermites are much slower than CHNO Systems;

- Smaller thermites are faster => Nano

Motivation




Metastable Interstitial Composites

MoO3, CuO, etc.Al

Al2O3

• How can we study the reactivity of nanocomposites ?

AlCuO??????

Al203




A New Approach: T-Jump Mass Spectrometry/Optical Emission

I or RI or RI or R

Mass-Spec Optical Emission

Fine wire coated and rapidly heated

Basic Approach:

Coat wire with:• Organics, • Organics+ binder• Thermites,• Thermites + organics• Sputtered thin films• Etc.

Photonsionse-

How to characterize the reactivity of powder of ultrafast nanocomposites ?




T-Jump Wire IgnitionExample of heating rate of 1.7 X 105 C/s

Wire temperature determined by resistance.

Tem

p (K

)

Norm

alized Intensity (a.u.)

Time (ms)

400

600

800

1000

1200

1400

1600

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7 8

Temp 6 11:50:52 AM 10/24/2008

Ignition temperature ~ 1250 K




Positively charged ions accelerated by Electric field move up time-of-flight tube to the detector

Detector

V

Oscilloscope Computer

V

T-Jump Mass-Spectrometry

Electron Gun

Vp

Possibility to study the ignition kinetics of Nanocomposites using mass spectrometry.

CAN BE PULSED UP TO 20kHz,to obtain multi-mass spectra from each combustion event.




Ignition of NanoThermite in T-Jump Mass-Spec:

High speed video 33,000 fps

Al + CuO => Al2O3 + Cu

70 µ

m

High Speed X-Ray Movie, 135,000 fps (total time = 1.8 msec)

Obtained at Argonne National LabCollaboration with T. Hufnagel , JHU.




Time Resolved Thermite Mass-SpectrumStoichometric Al/CuO- one spectrum every 100 µs.

Al/CuO nanocomposite under heating rate 8.8 ×105 K/s

Al +CuO => Al2O3 + Cu




0

100 H2O+

N2

+

O2

+

(a). background

0

200

CO2

+

Al+

H2O+

O2

+

Cu+

Al2O+

(b). Al/CuO thermite

0

200

0 20 40 60 80 100

CO2

+Al+

H2O+

Al2O+

Fe+

(c). Al/Fe2O

3 thermite

M/z

Background:H2O mass 18N2 mass 28O2 mass 32

Al/CuO thermiteOxygen species mass 16, 32Al mass 27Cu mass 63,65Al2O mass 70

Al/Fe2O3 thermiteAl mass 27 Fe mass 56Al2O mass 70

All have:CO mass 28CO2 mass 44

Difference between two systems: Oxygen species

Al2O is reaction product

More Details in Thermite Spectra Al +CuO => Al2O3 + Cu




0

50

100

150

200

800

900

1000

1100

1200

1300

1400

1500

1 1.5 2 2.5 3 3.5 4 4.5 5

Oxygen release from CuO, Fe2O3, ZnO

Inte

nsity

(a.u

.)

Temperature (C

)

Time (ms)

Cuo TempZno TempFe2O3 Temp

O2 from CuO

O2 from Fe2O3

O2 from ZnO

Temp ofCuO O2 release

Temp ofFe2O3 O2 release

Reactivity From Pressure Cell:CuO >> Fe2O3 >> ZnO (doesn’t even burn)

Oxidizer Decomposition (Melting) Point:CuO < Fe2O3 < ZnO

Results suggest that oxidizer decomposition to release O2 is important for ignition and that the amount of O2 release correlates with the reactivity.

Comparison of O2 Release from CuO , Fe2O3, ZnO

Gas Release from CuOX-Ray 135,000 fpsTotal time = 3 msec.




800

1000

1200

1400

1600

800 1000 1200 1400 1600

O2 R

eleas

e Te

mp

(C)

Ignition Temp (C)

Al/SnO2

Al/WO3

Al/Fe2O

3

Al/CuO

O2 Release Temperature vs. Ignition Temperature

There is a strong correlation between O2 release and the ignition temperature.

Comparing thermite ignition with O2 release from the neat oxide powders:




0 10 20 30 40 50 60 70 80

m/z

Al2O

CuAl

O2

CO2O

Al2O

CO2AlOO

2

Al

CuO

Al/CuO(Fuel RichEq ratio=3)

Al/CuO(Stoichiometric)

Enhanced PeaksAl

AlO (new peak)Al2O

Diminished PeaksO, O2

CO2

Cu

-Shift from excess oxidizer (high O2 peak) to excess fuel (high Al peak)

Fuel Rich VS Stoichiometric




How does the Al get out, since it has an oxide shell ?

We have observed hollow particles observed in Oxidation of Nanoaluminum

Diffusion mechanism for nano-aluminum•Molten aluminum diffuses outward.•Aluminum reacts with oxygen.

Hollow Product

MDM was proposed to explain the high reactivity in MICs (Levitas et al. 2006, 2007)

Molten Al Spallation of alumina shell

Molten Al clusters

Aluminum particle with core shell structure

Melt Dispersion




What is Role of Oxide Thickness on Reaction Time

Al nanoparticles ( ~50 nm dia) usually have an oxide shell of ~ 2nm.

50 n

m Oxide shellAl core

Al particles are oxidized @ 400 C for different lengths of time :a) 6 mins - 3 nm shell (based on wt. gain)b) 12 mins - 4 nm shell

Prepare Al with different Oxide Shell thickness

50 n

m




Ignition Delay vs Oxide Shell Thickness

- Ignition delay increases with shell thickness- Suggests a transport limit

Tem

pera

ture

(K)

Norm

. Intensity (a.u.)

Time (ms)

2 nm

Pulse turned off

4 nm

400

600

800

1000

1200

0

0.2

0.4

0.6

0.8

1

0 1 2 3 4 5 6 7

3 nm




Effective diffusion coeff., Deff = L2/ t

2 nm

50 n

m

L (nm) t (us) Deff (cm2/s)2 80 5e-10

3 480 1.9e-10

4 1000 1.6e-10

Steady State Temperature = 730 K

Mass spectrometric data shows same trend in ignition delay

Effective Diffusion Coefficient in Oxide Shell from Ignition Delay

Del

ay ti

me

(us)

Shell thickness (nm)

0

500

1000

1500

2000

1 2 3 4

No Steady State

Tsteady = 730 K

Ignition Delay Time

0

500

1000

1500

2000

1 2 3 4

No Steady State

Tsteady = 730 K

MS_Cu Signal

Effective Diff. Coeff. are consistent.

Park et al., J. Phys. Chem. B, 2005D= 10E-8 – 10E-9 cm2/sec

Vashista and co-workers 10E-6 cm2/sec

Ignition Delay Time




NanoCrystals of Al

Hi-Res Image

FeOMn

Elemental Map

Core-Shell Reactive Oxidizers

KMnO4

Fe2O3

KClO4

CuO

Coating Al with Ni

Al coated with Perfluorohexadecanoic Acid




Conclusions• Development of new mass spectrometry tool enables us to probe reaction dynamics of ultra-fast condensed state systems at high heating rates.

• Metal oxides appear to release O2 and the ignition temperature would appear to correlate with O2 release. However, some other systems not discussed today show indications of heterogeneous reactions.

• Al from oxide coated particles seem to leak out by a diffusion mechanism.

• A very short transient ion generation pulse ( 20 us) occurs just at the ignition point ( not discussed today)

• New classes of nanocomposites offer opportunities to tune reaction profiles.

Publications may be downloaded from www.enme.umd.edu/~mrz

Documents

Michael R. Zachariah - UMD