New Tools for Measuring the Reactivity of Energetic Materials

L. Zhou, K. Sullivan, N. Piekiel, S. Chowdhury, M. R. Zachariah

www.enme.umd.edu/~mrz

Department of Mechanical EngineeringDepartment of Chemistry and Biochemistry

Support

6.80*10-24Reddy & Cooper, 1977

7.4*10-9 (for 10 nm rad. Particle) (not at 1200 C)

Campbell et, 1999 (MD)

5.45*10-21Oishi & Kingrey, 19608.41*10-27Reed & Wuensch, 1980

1.09*10-19Lessing & Gordon, 1977

Value at 1200 C, m2/sExpression of D, m2/sSource

)/543400(09.2 RTExpD −=

)/785840(104.6 1 RTExpD −×=

)/240768(109.1 12 RTExpD −×= −

)/608580(1066.2 2 RTExpD −×= −

Diffusion Coefficient of Oxygen in Alumina

Diffusion Coefficient of Al in Alumina

1.5*10-19 at 773 KGarcia-Mendez et al, 19801.2*10-8 (for 10 nm rad. particle) (not at 1000 K)

Campbell et, 1999 (MD)

4.1*10-35Gall & Lesage, 1994 Value at 1000 K, m2/sExpression of D, m2/sSource

)/849282(103.1 10 RTExpD −×=

Huge discrepancy in the transport properties in literature

1. New Ion-Mobility MethodsA. Ni OxidationB. Surface Energy of Zn

1. New “T-Jump Mass-Spectrometry” ApproachA. NitrocelluloseB. RDXC.High Nitrogen Organics

OUTLINE

We have new materials and materials classes, it thus stands to reason that we need new (EXPERIMENTAL) tools to study them.

Primary Question: What is the nature of nanoscale materials combustion.i.e. Architectures, Mechanisms and Scaling laws

How can we come to terms with the size dependence Issue ?

Characterizing Nanoparticles Using Ion-Mobility

• Prepare particles of known size,• Measure their size and mass, • Determine how it changes with time in a reacting system.

HVcarriergas Polydisperse

nanoparticles

Mono-Surface areaParticles

• A Differential Mobility Analyzer ( DMA) selects particles based on electrical mobility.

2

1

pp

drage

dEvelocitymobilityelectricalZ

FF

∝=≡

=

CHARGED

→← drage FF

70 nm Ag particles Deposited on Charged Substrate

Differential Ion-Mobility: Gas-phase Electrophoresis

Mass classified aerosol exit

Aerosol Particle Mass analyzer (APM)

Outer electrode

Z

Aerosol entrance

w

Inner electrode

r2r1High voltage

(Ehara et al., 1997)

Aerosol entrance

mr d r neEvetrue APMω π ρ ω2

32

6= =

Fundamental measurement of particle mass

High Voltage

qE

2ωmr

Another Approach: Measure Total Mass or Change in Total Mass

Nickel Nanoparticle Synthesis and Size-resolved Oxidation Kinetics Study

ωAPM

CPC

Computer

Neutralizer

Sintering Furnace~1100 oC

~ 25 - 1100 oC

Tube FurnaceIsothermal Reactor

Air 0.5 lpm

Electrostatic Particle Sampler

DM

A2

CO

Carry gas A

r

Dilution flow

Tube FurnaceIsothermal Reactor

~400oC~50oC

Ni(CO)4Nickel packed bed

DM

A1Ni particles 0.5 lpm

Neutralizer

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

35 40 45 50 55 60

25oC 700oC1100oC500oC

Nor

mal

ized

Num

ber C

once

ntra

tion

Dp (nm)

Initial Size:40nm

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

50 60 70 80 90

25oC 700oC1100oC500oC

Nor

mal

ized

Num

ber C

once

ntra

tion

Dp (nm)

Initial Size:62nm

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

70 80 90 100 110 120

Nor

mal

ized

Num

ber C

once

ntra

tion

Dp (nm)

25oC 700oC1100oC500oC

Initial Size:81nm

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1 10-19 2 10-19 3 10-19 4 10-19 5 10-19

25oC

700oC

Mass (kg)

Nor

mal

ized

Num

ber C

once

ntra

tion

Initial Size:40nm

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

4 10-19 8 10-19 1.2 10-18 1.6 10-18 2 10-18

25oC

700oC

Nor

mal

ized

Num

ber C

once

ntra

tion

Initial Size:62nm

Mass (kg)

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 1 10-18 2 10-18 3 10-18 4 10

25oC

700oC

Nor

mal

ized

Num

ber C

once

ntra

tion

Mass (kg)

Initial Size:81nm

Tandem-DMA and DMA-APM ResultsD

MA

-APM

Tand

em-D

MA

0 200 400 600 800 1000 1200

40 nm62 nm81 nm96 nm

Ave

rage

Den

sity

(g/c

m3 )

Density of Ni

Density of NiO

Density of Ni2O

3

9

8

7

6

5

4

Temperature (oC)

from combination of both size ( TDMA) and mass change (DMA-APM)

The average density profile show a transition of Ni2O3 →NiO

Density

1

10

100

30 40 50 60 70 80 90 100

400 oC

500 oC

600 oC

700 oC

y = 0.0079 * x^(1.6) R= 0.96

y = 0.011 * x^(1.3) R= 0.89

y = 0.058 * x^(0.71) R= 0.82

y = 0.0013 * x^(1.4) R= 1

Bur

n Ti

me

(s)

Dp (nm)

1

10

100

30 40 50 60 70 80 90100

400 oC

500 oC

600 oC

700 oC

y = 0.0013 * x^(1.5) R= 0.88

y = 0.00095 * x^(1.8) R= 0.87

y = 0.00018 * x^(2.4) R= 0.96

y = 0.0022 * x^(2) R= 1

ΔM

/Δt x

10-1

6 (g/s

)

Dp (nm)

Mass rate Burn time

Burning Rate and Times

Ni Particle oxidation does not follow D2 => more like D1.4

Consistent with Al nanoparticle ~ D1.6 Combustion Theory and Modeling (2006)

Nickel Nanoparticle Oxidation Kinetics

Two different slopes show reaction regime and phase transition regime.

Smaller particles have smaller activation energy

Effe

ctiv

e D

iffus

ion

Coe

ffici

ent c

m2 /s

ec

Nickel Nanoparticle Oxidation Kinetics

Kinetically Ni is more reactive than AlAlthough releases less energy

Surface Energy Measurement of Nanocrystals

Al + MO => Some Experimental Results

0.09330270.011116412.6Fe2O3

0.07037080.01483111.8WO3

0.38626492.126.152.6SnO2

0.35830404.218.472.9CuO

GasMol Frac

T Ad

(K)

Pressurizationrate

(psi/usec)

Rise Time

(usec)

PressureRise (psi)

Pressurization Rate = Func ( Gas, T , dP? )

-The experimental pressure rise seems to correlate with the equilibrium gas prediction.Note: Rise Time is Drastically Different between CuO andFe2O3.

0

1

2

3

4

5

0% 20% 40% 60% 80% 100%

% WO3 by mole

Nor

mal

ized

Pre

ssur

izat

ion

Rat

e

0.00

0.05

0.10

0.15

0.20

0.25

0% 20% 40% 60% 80% 100%

% WO3 by mole

Mol

e Fr

actio

n

3000

3200

3400

3600

3800

Tem

pera

ture

(K) Al, AlO, Al2O

OWO, WO2, WO3ZnTotal GasTemperature (K)

Al + WO3 + ZnO ZnO is a very poor oxidizer.

But when added as a minor component can enhance combustion.

High Zn vapor concentration.

In general however we employ bulk thermodynamic properties.

Surface Energy and Nanocrystals

Surface energy and Nanocrystals:Surface energy plays an essential role in:- Melting- Coalescence- Evaporation and condensation.

Definition of surface energy:Surface energy is the energy required to create a unit area of new surface.

So What ?

While there are many theoretical studies on surface energy, there are only a few studies that reported the measured surface energy of nanocrystals.

Most experimental surface energy data stems from surface tensionmeasurement in the liquid phase and then extrapolate to solid.

=> At best this would give a result for a amorphous solid, not a crystal. [Vitos, et al., Surf. Sci., 186, 1998]

Why us:Our capability to manipulate small particles on the fly offers the opportunity to extract the surface energy from solid nanocrystals.

Experiment to Measure Surface Energy of Zn Nanocrystal

ωAPM

HEPA

DM

A

Exhaust flow

Zn aerosol 0.5 lpm

Zn NC Generation FurnaceIsothermal Reactor

~ 250 - 400 oC

Evaporation FurnaceIsothermal Reactor

~550oC

CPC

Neutralizer

Computer

TSI Particle Sampler

Excess flow

Carrier gas Ar~ 1 lpm

Experimental system for Zn, generation, size selection by DMA,evaporation and subsequent mass analysis with the APM.

TEM Images of Zn Nanocrystals

A. B.

C.

100nm mobility size Zn nanocrystals generated by condensation-evaporation method after DMA size selection

100nm

100nm

200nm

Basal planedepositionof Zn crystal

DMA-APM Measurement of Zn Nano-Crystal Evaporation

0

0.2

0.4

0.6

0.8

1

1.2

0.25 0.3 0.35 0.4 0.45

Room T250C275C300C325C350C375C400C

Nor

mal

ized

Num

ber C

once

ntra

tion

Particle Mass (fg)

Zn particle mass distributions for Zn evaporate at different temperatures

50 nm

For Zn, can detect a mass change < 0.01fg.

Uncertainty in precision for mass measurement ~ 2%

Onset Temperature of Evaporation

The onset temperature of evaporation is plotted against the inverse of theparticle size. The solid line is the least-squares fit to the experimental data

8

8.5

9

9.5

10

0 100 200 300 400 500

Part

icle

Mas

s (0

.1 fg

)

Temperature (C)590

600

610

620

630

640

650

0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 0.022

y = 666.06 - 3537.1x R= 0.99

Ons

et te

mpe

ratu

re o

f eva

pora

tion

(K)

1/Dp (nm-1)

Kinetic Model

• Evaporation rate to the temperature dependent surface energy.

• Zn NC surface energies are calculated to be 11.2 and 16.1 J/m2

at 3750C and 350 0C, respectively.

2/11

)2()(

TkmppSv

dtdm

Bm

dm

πρα −

=

Where pd = vapor pressure of the condensing species given by Kelvin equation:

)4exp(RTd

Mpp sd ργ

=

The mass change rate of the Zn NC is given by:

Comparison of Kelvin effect calculatedfrom our data of surface energy for

Zn NC and reference data for bulk Zn

1

10

100

0 50 100 150 200

Particle Mobility Diameter

Pd/P

s

Surface energy=12J/m2

Surface energy=1J/m2

Particle Size (nm)

s

d

pp

1

10-

100-

Experimental surface energy

Bulk

0 50 100 150 200

Developing a new type of Mass Spectrometry/Optical Emission to

study Ultra Fast Solid-State Reactions

Developing a new type of Mass Spectrometry/Optical Emission to

study Ultra Fast Solid-State Reactions

“T-Jump Mass Spectrometry”“T-Jump Mass Spectrometry”

Develop new diagnostic tool to measure how new molecules fall apart and the chemical reaction times of energetic systems

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.

Similar to Ed Dreizen

Photonsions

T-Jump Wire Ignition

Example of heating rate of 105 C/s

Wire temperature determined by resistance.

Ignition temperature ~ 800 C

Positively charged ions accelerated by electric field move up in time of flight tube to the detector

Detector Oscilloscope Computer

Electron Gun

• Temperature Jump T1 ~15 ms (5 ms ~ 100 ms adjustable)

• Cycle Time T2 ~1 ms (up to 5 us)

• EI Ionization Time T3 ~5 us (50 ns to 12 us adjustable)

•Rise and Fall time ~10 ns

Temporal Mass-SpectrometryCan generate Multiple Mass Spectrum from a single heating event

Linear Motion Feedthrough

Electron gun

Flight-tube

Gate valve

Coated Platinum Filament

T-Jump Mass-Spectrometer

0 10 20 30 40 50 60 70 80

T = 1.1 ms

T = 1.5 ms

T = 2.0 ms

T = 7.0 msT = 6.0 msT = 5.0 ms

T = 4.0 ms

T = 2.5 ms45

30

29

26

NO

T-Jump MS of Nitrocellulose

First:Mass 28 COMass 29 CHOMass 31 HNO Mass 45 HCO2

ThenMass 30 NOMass 46 NO2

NO2HNONO

HCO2

RO(NO)2 => RO + NO2RO + NO2 => ROO. + NOROO. => HCOO + R’

0

2

4

6

8

-2 0 2 4 6 8 10

Experiment 1Peak 27Peak 28Peak 29Peak 30Peak 31Peak 32Peak 45Peak 46

Time (ms)

-0.5

0

0.5

1

1.5

2

2.5

3

-2 0 2 4 6 8 10

Experiment 3 Peak 27Peak 28Peak 29Peak 30Peak 31Peak 32Peak 45Peak 46

Peak

27

Time (ms)

Nitrocellulose: Effect of Heating Rate

Low Heating Rate

High Heating Rate

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60 70 8

Inte

nsity

(a.u

.)

m/z

0

200

400

600

800

1000

0 0.5 1 1.5 2 2.5 3

RDX Heating Temp

Tem

pera

ture

(deg

. C)

Time (ms)

1.0 ms

1.5 ms

2.0 ms

2.5 ms

RDX

Heating rate = 1.5 X105 C/s

Sample courtesy of R. Doherty, NSWC-IH

N=N

CH2

42

Products Mass

NO2 46

NO,or CH2O 30

N2 or CH2N 28

H2CN

N OO

H75 or 74

RDX

or N=C=O

No evidence for:CH3NHONON2O

CHO from CH2O 29

HCN 27

120 ( also seen by Y.T. Lee)

56

(NO2)-NCH2-NO2 + = RDX – NO2

Large signal

Large signal

+ 2 NO2

+

N2 + CH2

42CH2

CH2

CH2

74

CH2

O

Revised NO2 Dissociation PathwayRevised NO2 Dissociation Pathway

Goddard

R. Behren, Sandia will provide iosotopecally labeled RDX

N

N

N

N C

C

NO2

NO2

NO2

NH 2

CH

H 2H

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60 70 80

1 ms

1.5 ms

2 ms

MIG-1

N

42

43

Sample provided byProf: Thomas KlapoetkeUniversity of Munich

N

N

N

N

NNO2

H

H

800

1000

1200

1400

1600

1800

2000

0 10 20 30 40 50 60 70 80

0.7 ms

1 ms

1.5 ms

2 ms Sample provided byProf: Thomas KlapoetkeUniversity of Munich

4356

HN=NH + N2

800

900

1000

1100

1200

1300

0 10 20 30 40 50 60 70 80

1.6 m s

2.0 m s

2.5 m s

btnm m oxam ide

46

42

45

28

29

30

31

32

18

Sample provided byProf: Thomas KlapoetkeUniversity of Munich

42

30

SUMMARY• New material types ( nanoscale materials, new molecules) may under some circumstances require specialized tools to characterize their fundamental properties and reactive behavior.

• Ion-Mobility: Here we demonstrate its applicability to the reactivity and surface properties of nanoparticles.

• T-JUMP Mass-Spectrometry: Opportunity to probe the reaction dynamics at fast time scales.

SURGEON GENERALS WARNINGIn the absence of experimental validation a modeling result if repeated often enough becomes a fact.

SURGEON GENERALS WARNINGIn the absence of experimental validation a modeling result if repeated often enough becomes a fact.

Particularly as it relates to new materials the ability to use computation exceeds the capability to implement experiments to elucidate microscopic properties and details.