NEEM MURI

NANO ENGINEERED ENERGETIC MATERIALS MURI

Richard A. YetterThe Pennsylvania State University

Workshop on NanoEnergetics at RutgersRutgers University, Busch Campus, Biomedical Engineering Building

599 Taylor Road,Piscataway, NJ 08854-561028 February 2008

Synthesis & Assembly

Theoretical Modeling &Simulation

Experimental Characterization &

Diagnostics

NEEMna

no -

mac

ro

mac

ro -

nano

nano - macro

PSUUIUC

USCPSU

UIUCPSU

NEEM MURI MURI Team Members

• David Allara, PSU, Department of Chemistry • Ralph Nuzzo, UIUC, School of Chemical Sciences• Dana Dlott, UIUC, School of Chemical Sciences• Greg Girolami, UIUC, School of Chemical Sciences• Priya Vashishta, USC, Departments of Chemical Engineering and Material

Sciences, Physics and Astronomy, and Computer Science• Rajiv Kalia, USC, Departments of Chemical Engineering and Material

Sciences, Physics and Astronomy, and Computer Science• Aiichiro Nakano, USC, Departments of Chemical Engineering and Material

Sciences, Physics and Astronomy, and Computer Science• Vigor Yang, PSU, Department of Mechanical and Nuclear Engineering• Richard Yetter & Grant Risha, PSU, Department of Mechanical and Nuclear

Engineering• Kenneth Kuo, PSU, Department of Mechanical and Nuclear Engineering• Steven Son, LANL-Purdue, 2005-2006 Sabbatical Leave at PSU

NEEM MURI Objectives

• Develop new methodologies to assemble nano-energetic materials that provide concurrent increases in performance and managed energy release rate while reducing sensitivity.

• Obtain fundamental understanding of the relationship between the design of nano-engineered energetic materials and their reactive and mechanical behaviors

NEEM MURI Critical Technology Issues

• Self-assembly and supramolecular chemistry of the fuel and oxidizer elements of energetic materials have lagged far behind chemistries in other disciplines (such as pharmaceuticals, microelectronics, microbiology).

• There is no fundamental understanding of what type of supramolecular structures provide desirable performance in combustion, mechanical, and hazard characteristics.

NEEM MURI An Integrated, Systematic Approach

polymer binder

nano-metallicparticle

micron-crystallineoxidizer

nano-crystallineoxidizer

nano-energetic materials

nano Al & Bno RDX, HMX, & ADNcarbon nanotubes

self-assembledmicron-to-millimeter scale

energetic structure

self-assembledenergetic material

with gradient in chemical composition

conventionally assembledenergetic material with

micron-to-millimeter scale energetic structures

NEEM MURI Program Philosophy

• Bring together scientists and engineers in nanotechnology and propellants and explosives

• Couple multiscale modeling and multiscale diagnostics• Research and develop new concepts for assembling and

understanding the dynamics of nano engineered energetic materials

NEEM MURI Program Structure and Interactions

Synthesis & Assembly

Theoretical Modeling &Simulation

Experimental Characterization &

Diagnostics

NEEM

nano

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acro

mac

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nano

nano - macro

PSUUIUC

USCPSU

UIUCPSU

NEEM MURI

Synthesis, Self-Assembly, and Supramolecular Chemistry of Nano-

Structured Energetic Materials

NEEM MURI SAM-coated Al and B nanoparticles

Starting point: Fabricate high-energy Al or B nanoparticles with surface-bound self-assembled monolayers (SAMs)

Q: What is the optimum particle size and passivation layer?

NEEM MURI Synthesis and Assembly

• Synthesis of Al nanoparticles in presence of 3 potential passivating agents: polyethylene, heptaldehyde, trioctylaluminum.

• Synthesis of the nanoclusters [AlCp*]4 and K2[AliBu]12.• Boron nanoparticles synthesized: gas-phase pyrolysis of

decaborane/Ar at 700-900oC at 1 atm, nanoparticles are pure (>97%B), easily suspended in organic solvents, and show diffraction peaks of β-rhombohedral boron with 20nm domain size.

• RDX nanoparticles produced via supercritical processing (RESS): particles sizes from ~90-300 nm achieved, high pressure CO2solvent (30,000psi), particle collection via dry ice

• Aromatic and aliphatic nitro monolayers formed and reactivity studied. Aluminum oxynitride products formed with no degradationof aromatic ring.

• Al nanofilaments of ~2-3 atom diameters grown and stabilized within inert monolayer matrices

• Self-assembled ordered microspheres of a nanoscale thermite fabricated.

nB

nRDX

nAl-nCuOcomposite

NEEM MURI TEM images of boron nanoparticles Nuzzo and Girolami, UIUC

• Majority of particles are 10 – 50 nm in diameter• Spherical shapes, not highly crystalline (electron diffraction

suggests a large amorphous fraction)• No surface oxide coating (essentially elementally pure B)

NEEM MURI DSC traces of boron nanoparticles under O2 atmosphere- Nuzzo and Girolami, UIUC

• Boron nanoparticles are relatively resistant to oxidation, no significant oxidation up to 430 °C

• Sudden exotherm maximizing (once) at ~570 °C (the next measurement destroyed the DSC)

• Total heat evolved by first sample was ~30 % of calculated value—recovered material still largely B but now passivated by formation of oxide overlayer

0 100 200 300 400 500 600 700

0

10

20

30

40

50

60

17.2 kJ/g431 oC 643 oC

576 oC

Hea

t flo

w (W

/g)

Temperature (oC)

NEEM MURI Self-Assembled Nanoscale Thermite Microspheres

~4 µm

60nm 100nm

nAl (38nm) nCuO(33nm)

nAl-TMA nCuO-MUA

• Create Self-Assembled Monolayer (SAM) on surface of individual particles

• Monolayers contain a functionalized group at tail end (either + or – charged)

• When mixed in a diluted and slightly elevated temperature they form macroscale structures with nanoscale constituents

Kalsin et al., Science, v312, 2006

NEEM MURI

Theoretical Modeling of Nano-Structured Energetic Materials from the

Atomistic/Molecular Scale to the Macroscale

NEEM MURI Coupled FE/MD/QM Simulations Vashishta, Kalia, Nakano – USC & Yang -PSU

Approach:• Finite element (FE)• Atomistic molecular dynamics (MD)• Quantum-mechanical (QM) calculation based on density functional theory (DFT)• Couple Relevant Processes at Micro and Meso Length Scales to Macroscale Phenomena

Challenge: Seamlessly couple QM scheme & MD approach based on effective interatomic potentials

Collaboratory for Advanced Computing & Simulations (CACS)• 1,512 processor Intel Xeon Linux cluster at USC• 2.4 million processor-hours of computing on IBM SP4 & Compaq AlphaServer at DoD Major Shared Resources Centers

Multiscale QM/MD/FE simulation (top) implemented on a Grid (bottom) of supercomputers, data archive, and virtual environment

NEEM MURI Theoretical Modeling and Simulation

•Reactive MD simulation of flash heating of an oxidized Al nanoparticle reveals rapid melting & evaporation of the Al core followed by expansion & eventual failure of the oxide shell.

•MD simulation of shock compression of alkanethiol self assembled monolayers (SAMs) reveals shock-induced inversion of “even-odd” effect in gauche-defect density.

•Calculated the nonlinear elastic properties of nanocrystalline RDX.

•Performed nanoindentation simulation on RDX.•Melting temperature of nAl dependent on particle size, melting temperature of alumina also strongly dependent on size.

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NEEM MURI Nano Aluminum Particle OxidationVashishta, Kalia, Nakano - USC

Metal Oxide Core-Shell Structure

Oxide thickness saturates at 40Å after 0.5 ns – good agreement with experiment (Nieh et al., Acta mater. 44, 3781 (1996)

Oxidative Percolation

OAl4 clusters percolate to form a neutral shield around Al nanoparticle, which impedes oxidation

No heat dissipation allows rapid T increase in surface and core. Larger spheres correspond to oxygen and smaller spheres to aluminum; color represents the T.

Oxidation Under Closed Conditions

Number of Atoms: ~ 250,000 Al, ~ 550,000 O; Initial Al cluster 100Å radius

NEEM MURI Dynamics of Oxide Growth Vashishta, Kalia, Nakano - USC

NEEM MURI Local Stresses During Oxide Growth Vashishta, Kalia, Nakano - USC

NEEM MURI

Experimental Characterization of Reactive and Mechanical Behaviors

of Nano-Structured Energetic Materials

NEEM MURI Dynamics of a NEEM

fuel

oxidizer

passivation

3 (or more)part structure

activation initiation ignition

nascentpropagation

steadypropagation

100 nm

NEEM MURI

fuel

oxidizer

passivation

structure initiation ignition

transientpropagation

steadypropagation

activation

100 nmflash-heatingSFG

time-resolvedIR

time-resolvedemission

time-resolvedemission

NEEM MURI Experimental Characterization and Diagnostics

•Real-time vibrational spectroscopy of flash-heated nanoenergetic material.

•Real-time measurement of emission of flash-heated nanoenergetic material.

•Ultrafast dynamics of SAMs on metal surfaces with flash heating, studied by nonlinear coherent vibrational spectroscopy.

•Characterization of nanoscale thermite combustion (for variable particle sizes and pressures) reveals the importance of physical properties and gas-generation on propagation speed and ignition.

•Combustion analysis of nAl-liquid oxidizer (CH3NO2, H2O, H2O2) mixtures reveals high burning rates and high chemical efficiency of nanoingredients.

NEEM MURI Time and space resolved spectroscopy of nanoenergetic materials

Experimental measurements of engineered nanoenergetic materials dynamic response to heat and shock

Response of isolated nanoparticlesInteractions among nanoparticlesReaction propagation over short distances (100 nm to 1 mm)

Approach• Picosecond laser flash-heating of nanoenergetic materials

(Picosecond CARS, time-resolved emission, streakscope for long distance and directional propagation)

• Ultrafast (sub ns) microscopy of laser-initiated materials• Femtosecond IR laser, time resolved IR spectroscopy (C-H, C-C, Al-

O, Al-F, C-F, O-H, etc.)• Femtosecond laser-driven shock compression and shock

spectroscopy of nanoenergetic materials

NEEM MURI Pulsed thermal desorption of SAM passivation layers

SFGprobe(1 ps)

glass

Al, Au

100 fs laser

heatingpulse

vis

IR

SFG

heat to melting point in <5 picoseconds

ActivationActivation SFG is the only technique that can probe monolayers with picosecond time resolution

nonlinearcoherent

• Ordinarily SAMs desorb at 100-200°C• Flash-heating to melting point 700-1000°C for 10 nanoseconds produced no

SAM desorption• Extraordinary stability of SAMs to pulsed heating• Opens up a new field of research in molecular dynamicsZ. Wang, J. A. Carter, A. Lagutchev, Y. K. Koh, N.-H. Seong, D. G. Cahill, and D. D. Dlott, Ultrafast flash thermal conductance of molecular chains, Science 317, 787-790 (2007).

CH3-(CH2)17-SHon gold

CH3-(CH2)16-CO2Hon Al with oxide

NEEM MURI Time resolved images of Al + TeflonAF

flash heated by 100 ns pulses

computer &

video framegrabber

dye laser

delay generator

multimode optical fiber

progressive-scanCCD camera

N2 - laser

S

flash-heating pulseillumination pulse

100 ps Nd:YLF laserlens

BSShutter

PD DO

30.2

nm

Al 1

0%+T

eflo

n

50ns 100ns0 ns

200ns 300ns

150ns

500ns400ns

660 µm

laser pulse(invisible)

sam

ple

surfa

cereflectedimage ofsamplesurface(ignore)

shockwave in air

debris

note: 100 µm travel in 100 nsis 1 km/s

NEEM MURI Effect of dilution with Al2O3 nanoparticles on nAl/nCuO thermite propagation

0

2

4

6

0 300 600

0%5%10%15%

Posi

tion

(cm

)

Time of Arrival (µs)

% Al2O3 Peak Pressure (MPa) Velocity (m/s)

0% ~10 6335% ~9 57010% Bimodal ~2 and ~6-8 146-54415% Bimodal ~2 and ~6-8 (fewer

than at 10%)69-112

20% ~2 spiraling

-2

0

2

4

6

8

0.96 1 1.04 1.08 1.12

pressure 2pressure 5

Pres

sure

(MP

a)

Time (ms)“The Effect of Al2O3 Nano-Particles on an Al-CuO Nano-scale Thermite,” Malchi, J.Y., Foley, T.J., Yetter, R.A., and Son, S. F., Combustion Science and Technology, 2007.

NEEM MURI Effect of ambient pressure on nAl/nCuO thermite propagation

0

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0 5 10 15

Pre

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Osc

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1

10

100

1000

0 5 10 15

V f[m/s

]

Pa[MPa]

Osc

illat

ing

0

0.02

0.04

0.06

0.08

0 0.001 0.002 0.003

4.60 MPa Argon5.50 MPa Argon

Pos

ition

[m]

Time [s]

0

0.02

0.04

0.06

0.08

0 4 10-5 8 10-5

0.69 MPa1.24 MPa1.65 MPa1.68 MPa

Posi

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[m]

Time [sec]

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0 5 10 15

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He He

NEEM MURI nAl/H2O Combustion

0.1

1

10

0.1 1 10B

urni

ng R

ate

[cm

/s]

Pressure [MPa]

rb [cm/s] = 4.5*(P[MPa])0.47

ADN* CL-20*

HNF*

JA2#HMX* * Altwood, 1999

# Kopicz, 1997

0.1

1

10

0.1 1 10

38nm Al - H2O

38nm Al - H2O / Poly-A

80nm Al - H2O

130nm Al - H2O

Ivanov et al. 1994(UFP Al-H

2O / Poly-A)

rb (80-nm Al, cm/s) = 1.203 * P0.27

rb (130-nm Al, cm/s) = 0.680 * P0.31

Line

ar B

urni

ng R

ate

[cm

/s]

Chamber Pressure [MPa]

φ = 1.0

38-nm Al - H2O (Risha et al. 2007)

0

0

0 20 40 60 80 100 120 140Pressure [atm]

p

φ = 1.080

100

Dp = 38 nm

η che

m[%

]

φ = 1.0

NEEM MURI Additional Challenges

With the development of nano engineered energetic materials, as with any newly synthesized molecular energetic material, the quantities of material are usually limited and costly and the design variables unlimited. Hence,

1) New methods requiring minimal quantities of material are needed at early stages of development to characterize the performance and safety.

Optimization of nanoengineered energetic materials will occur over many years. However,

2) Integration of nanomaterials into practical systems needs to occur incrementally in a timely manner.