NEEM MURI
Multi-Scale Modeling ofMulti-Scale Modeling ofMulti-Scale Modeling of Nano Aluminum Particle Ignition and Combustion
Multi-Scale Modeling of Nano Aluminum Particle Ignition and Combustion
Vigor Yang, Dilip Sundaram, and Puneesh Puri Georgia Institute of Technology
Atlanta, GA 30332-0150and
The Pennsylvania State UniversityUniversity Park PA16802University Park, PA16802
Presented at 2010 MURI NEEM Program Reviewg
Aberdeen, Maryland
March 15, 2010
NEEM MURI
Multi-Scale Modeling of N Al i P ti l I iti d C b ti
Multi-Scale Modeling of N Al i P ti l I iti d C b tiNano Aluminum Particle Ignition and CombustionNano Aluminum Particle Ignition and Combustion
• Development of a unified model for ignition and combustion of aluminum i l li bl ll lparticles applicable at all scales
• Investigation of the essential difference in physiochemical mechanisms atmicro and nano scales St d f th ll ti b h i f ti l d t b ti i fl i t• Study of the collective behavior of particle dust combustion in flow environments
• Coupling the studies of the USC group at meso/micro scalesGT
Quantum Micro MesoNano Macro
USC
Q
Length (m)
10-12 10-9 10-6 10-3 100
NEEM MURI Various Stages of Particle Behavior
RoutO Anions Rout Rout
Rin
δAl Cations
Rint
δO2 Molecules
Rint
δO2Molecules
Phase TransformationsStage I
(particle heating/phase transformations)
Rin
Stage II(core melting and ignition due to melting/cracking)
Stage III(heterogeneous reactions/healing of cracks)
O2 Molecules
O id
Al (g)
oxidizer Al2O3(s)Al(s)Al(l)
Stage IV
melting of oxide layer to formcap (micro)
particle consumed due to heterogeneous reactions (nano)
Detached flame front
Oxide cap
Stage Vdetached flame front (micro)
Al2O3(s)Al(s)Al(l) detached flame front (micro)Al(l)
NEEM MURI Ignition Temperature of Single Aluminum Particle in Air as Function of Particle Size
Micron and larger size particles:
• For particles ( > 100 microns)
Micron and larger size particles:
• For particles ( > 100 microns)3500
Parr et al. [11]B li t l [36]
3500Derevyaga et al. [30]M h t l [29]For particles ( > 100 microns),
ignition occurs at temperature near the melting point of aluminum oxide (2350 K) F i l (1 100 )
For particles ( > 100 microns), ignition occurs at temperature near the melting point of aluminum oxide (2350 K) F i l (1 100 ) e,
K
2500
3000
Bulian et al. [36]Assovskiy [35]Yusasa e tal. [33,34]Brossard et al. [32]Ermakove tal. [31]
e,K
2500
3000
Merzhanov et al. [29]Friedman et al. [27,28]Trunov et al. [15]CurveFit
• For particles (1~100 microns), ignition over a wide range of temperature from 1300 to 2300 K
• For particles (1~100 microns), ignition over a wide range of temperature from 1300 to 2300 K
Tem
pera
ture
2000
2500
Tem
pera
ture
2000
2500
Nano size particles:
• Ignition reported to occur at temperature as low as 900 K
Nano size particles:
• Ignition reported to occur at temperature as low as 900 K
Igni
tion
T
1000
1500
Igni
tion
T
1000
1500
• Trunov et al. (2005) suggested that aluminum oxidation and polymorphic phase transformation of the alumina shell are responsible
• Trunov et al. (2005) suggested that aluminum oxidation and polymorphic phase transformation of the alumina shell are responsible 10-2 10-1 100 101 102 103 104500
1000
10-2 10-1 100 101 102 103 104500
1000
of the alumina shell are responsible for these diverse ignition temperatures
of the alumina shell are responsible for these diverse ignition temperatures
Particle Diameter, μmParticle Diameter, μm
NEEM MURI Burning Time of Single Aluminum Particle in Air as Function of Particle Diameter
Micron and larger size particles:
B i d diff i
Micron and larger size particles:
B i d diff i105
Wilson and Willams [27]• Burning under diffusion-controlled conditions
• Beckstead’s particle burning time correlation based on various
• Burning under diffusion-controlled conditions
• Beckstead’s particle burning time correlation based on various s 103
104
Wilson and Willams [27]Wong and Turns [29]Prentice [28]Olsen and Beckstead [30]Hartman [26]Friedman and Macek [21]
experimental measurements:experimental measurements:1.8
0.2 0.11 0
beff
dC T p X
τ =
ngtim
e,m
s102
103 Friedman and Macek [21]Davis [25]Parr et al. [9] (T0=1500 K)Parr et al. [9] (T0=2000 K)Models
d1.8
Nano size particles:
• Burning under kinetically-controlled conditions
Nano size particles:
• Burning under kinetically-controlled conditions
ffB
urni
n
100
101
1500 K
controlled conditions• d1-model from theoretical
prediction; however, d0.3 law based on experimental data of P l 2003
controlled conditions• d1-model from theoretical
prediction; however, d0.3 law based on experimental data of P l 2003 10-2 10-1 100 101 102 103
10-1
10d0.32000 K
3500 K
Parr et al., 2003 Parr et al., 2003 Particle diameter, μm10 10 10 10 10 10
NEEM MURIResearch Topics
• Phenomenological development of aluminum particle ignition and combustion over a wide range of length scales based on g gcharacteristic time and dimensional analysis.
• Molecular dynamics simulations of small aluminum particles– the effect of pressure and voids
the effect of the oxide shell– the effect of the oxide shell – the effect of a nickel coating
• Macroscale modeling of flame propagation– the ignition and combustion processes of nAl with liquid
oxidizers
NEEM MURI Ignition Criteria Heating, Cracking, and Healing of Oxide Layer
• Ignition at nano scale occurs at much lower temperature (~ 940K) than at micron scale
• Ignition at nano scale occurs at much lower temperature (~ 940K) than at micron scale
• Two schools of thoughts on ignition criteria at nano scale:– cracking due to thermal stress– polymorphic phase transformation of oxide layer
• Two schools of thoughts on ignition criteria at nano scale:– cracking due to thermal stress– polymorphic phase transformation of oxide layerp y p p y
• Characteristic time scales for heating, melting, and healing must be considered
• Fourier number ~ A/V
p y p p y• Characteristic time scales for heating, melting, and healing must be
considered• Fourier number ~ A/V
20* fg
meltp f
D ht
c Tα=
Δ
• If the characteristic time for shell growth through direct oxidation is small as compared to that of melting and cracking then the oxidation for the
Rout
δO2 Molecules2
* 0heat
f
Dtα
=
p f
2dN P Dπ
melting and cracking, then the oxidation for the rest of time can be modeled as that of diffusion through the layer.
• If the characteristic time for shell growth is larger the oxidation process must be modeled as
Rint
O2 Molecules
R2 2
2O O pdN P D
dt mKT
π
π=
larger, the oxidation process must be modeled as the direct attack of oxygen on aluminum surface with cracking.
Rin
NEEM MURI Mode of CombustionDiffusion vs. Kinetically Controlled
dρ
Diffusion ControlledDiffusion Controlled Kinetically ControlledKinetically Controlled2dρ
• To determine the dominant combustion mechanism a Damkohler number• To determine the dominant combustion mechanism a Damkohler number
0,
,2p
b kinp o
dt
MW kPXρ
∞
=0,
,8 ln(1 )p
b diffO
dt
D iYρ
ρ ∞
=+
• To determine the dominant combustion mechanism, a Damkohler number, Da, for surface reaction is defined as
• To determine the dominant combustion mechanism, a Damkohler number, Da, for surface reaction is defined as
, 0 ,b diff p ot MW kPd XDa ∞= =
• Small particles at low pressures burn under kinetically controlled conditions • Small particles at low pressures burn under kinetically controlled conditions
, ,4 ln(1 )b kin o
Dat D iYρ ∞
= =+
• Large particles and high pressures favor diffusion controlled mechanism.• The characteristic burning time follows d1 law and is inversely proportional
to pressure under kinetically controlled mechanism. The burning time
• Large particles and high pressures favor diffusion controlled mechanism.• The characteristic burning time follows d1 law and is inversely proportional
to pressure under kinetically controlled mechanism. The burning time p y gfollows the d2 law and is independent of pressure under diffusion controlled mechanism.
p y gfollows the d2 law and is independent of pressure under diffusion controlled mechanism.
NEEM MURI Mode of CombustionNano vs. Micron Scale
• Heterogeneous oxidation more favorable for nano particles as compared to a detached fl f i ti l
Rout
δ
O Anions
Al Cations
Al2O3(s)Al(s)Al(l)
flame for micro particles.• In case of direct oxidation, the process is
kinetically controlled due to small diffusion time scales.
Heterogeneous(diffusion controlled)
Rin
Phase Transformations R• In case of heterogeneous oxidation through oxide layer, the process is diffusion controlled due to slow diffusion of Al cationsor O anions through the oxide layer.
Rout
Rint
δO2 Molecules
• The melting and boiling points of aluminum are 933 and 2791 K, respectively; and for alumina, the melting and boiling points are2327 and ~3700 K.
Heterogeneous(kinetically controlled)
Rin
idi• For micron-scale particles, as oxide melts, Al can vaporize forming a detached flame. But if the rate of heterogeneous oxidation is very fast, particle can self heat to melting point
d t d i h tOxide cap
Al (g)
oxidizer
and get consumed in a pure heterogeneous fashion. Homogeneous (microscale)Detached
Flame front
NEEM MURI Fourier Analysis)
Al2O3(s)Al(s)Al(l)
O Anions
Al Cations
O Anions
Al Cations
me
scal
e(p
s
6
8
Core Melting/Fragmentation of Shell
Al Cations
Phase Transformations
Al Cations
Phase Transformations
acte
ristic
tim
4
Phase Transformations
O2 Molecules
Phase Transformations
O2 Molecules
O id hi k ( )
Cha
ra
1 2 3 4 5 6 7 8 9 10
2Melting of Shell/Heterogeneous Oxidation of core
Oxide thickness (nm)O2 Molecules
Al (g)
oxidizer
Detached flame front
Oxide cap
NEEM MURIVarious Regimes of Particle Ignition
NEEM MURI Characteristic Time Scale Study (I)
tmelt c> treac V1000 K, 1 atm
O Anions
Al Cations
Al2O3(s)Al(s)Al(l)
O Anions
Al Cations
O Anions
Al Cations
s(nm
)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
melt,c reac
tmelt c< tmelt sIIIV
V Al Cations
Phase Transformations
Al Cations
Phase Transformations
Al Cations
Phase Transformations
eth
ickn
es
100
melt,c melt,s
IIV V
Phase TransformationsPhase Transformations
O2 Molecules
Phase Transformations
Oxi
de
10-1
tmelt,s< treac
IIIVIVI
Core size (nm)20 40 60 80 100 O2 Molecules
Al (g)
oxidizer
Al (g)
oxidizer
Detached Flame front
Oxide cap
Detached Flame front
Oxide cap
NEEM MURI Characteristic Time Scale Study(Effect of Pressure)
m)
1
tmelt,s=tmelt,ctmelt,c=treactmelt s=treac
tmelt,c> treacV1000 K, 5 atm
m)
tmelt,s=tmelt,ctmelt,c=treac
tmelt,c> treacII V1000 K, 10 atm
deth
ickn
ess(
nm
100
101 melt,s reac
tmelt,c< tmelt,s
I
IIIV
IVV
deth
ickn
ess(
nm
100
101 tmelt,s=treac
tmelt,c< tmelt,s
III
IV
IV V
Core size (nm)
Oxi
20 40 60 80 100
10-1tmelt,s< treac
I
III VIVI
Core size (nm)
Oxi
d
20 40 60 80 100
10-1 tmelt,s< treac
I
VIVI
ess(
nm)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c< tmelt,s
V
1000 K, 50 atm
ess(
nm)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c< tmelt,s
V1000 K, 100 atm
Oxi
deth
ickn
e
10-1
100
tmelt,s< treac
IIIV
VI
Oxi
deth
ickn
e
10-1
100
t < t
III
V
Core size (nm)20 40 60 80 100
10 VI
Core size (nm)20 40 60 80 100
tmelt,s< treac
NEEM MURI
Molecular Dynamics Study of Melting of Nano Aluminum Particlesg
NEEM MURI Properties of Aluminum Particles at Nano Scales
• Aluminum particle of 1 nm consists of about 32 aluminum molecules. • A large fraction of constituent particles are on the surface • Aluminum particle of 1 nm consists of about 32 aluminum molecules. • A large fraction of constituent particles are on the surface • Melting and boiling temperatures of particles decrease with decreasing particle size.
Melting temperature could be as low as 400 K for 1-nm particle • Liquid and solid phases may coexist in dynamic equilibrium over a range of temperatures
• Melting and boiling temperatures of particles decrease with decreasing particle size. Melting temperature could be as low as 400 K for 1-nm particle
• Liquid and solid phases may coexist in dynamic equilibrium over a range of temperatures
K
1000
Aluminum melting temperature as function of particle size obtained by molecular dynamics simulations (Thompson et al.
Aluminum melting temperature as function of particle size obtained by molecular dynamics simulations (Thompson et al.
Tem
pera
ture
,K
600
800
2005), experiment measurements (Eckert et al., 1993), and theoretical predictions 2005), experiment measurements (Eckert et al., 1993), and theoretical predictions
Mel
ting
T
400
600 Bulk AluminumTheory [23]MD Simulations [22]Experiment [21]
Particle Diameter, nm0 100 200 300
NEEM MURI Melting Point of Nano-Aluminum Particle as Function of Size
• The melting point of aluminum nano-particles increases monotonically as a
• The melting point of aluminum nano-particles increases monotonically as a p yfunction of particle size and approaches bulk melting point for particle size of 8 nm and larger.
• Two body Lennard-Jones fails to
p yfunction of particle size and approaches bulk melting point for particle size of 8 nm and larger.
• Two body Lennard-Jones fails to ypredict the melting point. Sutton-Chen validated against structural properties also fails to capture the melting phenomenon.
ypredict the melting point. Sutton-Chen validated against structural properties also fails to capture the melting phenomenon.
• Glue and Embedded-atom potentials predict comparable melting points with results from Glue potential slightly higher in magnitude
• Glue and Embedded-atom potentials predict comparable melting points with results from Glue potential slightly higher in magnitude
ergy
,eV
-2.90
-2.85
-2.80Glue PotentialStreitz Mintmire PotentialSutton Chen PotentialEmbedded Atom Potential
• Equilibrium potential energy vs. temperature study done for clusters of aluminum atoms less than 800 atoms e.g. 256 atoms (2 nm). Dynamic coexistence of solid and liquid phase
• Equilibrium potential energy vs. temperature study done for clusters of aluminum atoms less than 800 atoms e.g. 256 atoms (2 nm). Dynamic coexistence of solid and liquid phase
Pote
ntia
lEne
-3.05
-3.00
-2.95
coexistence of solid and liquid phase was observedcoexistence of solid and liquid phase was observed
Temperature, K300 400 500 600 700 800
-3.10
NEEM MURI
Effects of Pressure and Void Size on Melting of AluminumMelting of Aluminum
NEEM MURI Different void geometries considered for defect-nucleated melting of 5.5 nm aluminum nano particle
0.00 nm3 0.32 nm3 0.98 nm3
2.94 nm3 4.91 nm3 6.88 nm3
8.84 nm38.19 nm3
NEEM MURI Effect of Void Size on Melting of 8.5 nm Aluminum Particle
1000ur
e(T
m)
950
Tem
pera
tu
850
900
Mel
ting
T
800
850
M
0 20000 40000 60000 80000750
Void Volume (A3)
NEEM MURI Evolution of density contours with time showing mechanism of melting for 8.5 nm nanoparticle
0.0 ps 90.9 ps 106.8 ps 119.1 ps
No Void
0.0 ps 91.8 ps 98.7 ps 109.8 ps
Void size of 5.0 nm3
0.0 ps 57.4 ps 93.9 ps 97.8 ps
Structural Collapse (20.0 nm3)
NEEM MURI Melting of Al Particle with Oxide Coating(8 nm Particle)
ex,δ 0.08
0.10
0.12
dex,δ
0.010
0.015
940 K
Lind
eman
nIn
de
0.02
0.04
0.06
Lind
eman
nIn
d
0.005
0.0 0~940 K
~1100 Kcore oxide
Iterations0 5000 10000 15000-0.02
0.00
Iterations0 5000 10000 15000
0.000
Aluminum oxide (Al2O3) may melt at a temperature (less than 1200K)substantially lower than its bulk value
NEEM MURI Thermo-Mechanical Behavior of Ni-Coated Nano-Al Particles
• Tight-binding force scheme (Cleri & Rosato); vacuum conditionE ilib i ti f b lk Al & Ni i NVE bl• Equilibrium properties of bulk Al & Ni using NVE ensemble
• Melting point & latent heat of melting of bulk Al, bulk Ni, nAl, & nNi particles with NPT ensemble– Homogenous melting at 1030 K (Al), 1880 K (Ni) -- no free surface for
liquid nucleation– Heterogeneous melting for nano-particles --inward propagating liquid phase
front
Cohesive Energy, eV Lattice Constant, Å Latent Heat of Melting, kJ/mol
Prediction Kittel et al. Prediction Kittel et al. Prediction Brandes & Brook
Al -3.3315 -3.339 4.043 4.05 9.65 9.82Al 3.3315 3.339 4.043 4.05 9.65 9.82
Ni -4.415 -4.435 3.474 3.519 18 17.16
NEEM MURINi-Coated Nano-Al Particles –Results (1/2)
• NPT calculations for Al core (3-10 nm), Ni shell (0.5-2 nm) to study thermo-mechanical behaviorThi k f h ll l ti t di t f
6 nm Al, 2 nm Ni shell
Lindemann index
• Thickness of shell relative to diameter of core → integrity of shell upon core melting
• Melting of core delayed due to cage-like effect -- Al t i t lli b d ith Ni th i t fatoms in metallic bond with Ni near the interface
• Inter-metallic reactions decrease potential energy --heat release
• 6 nm Al, 2 nm Ni – solid Ni withstands tensile stressTotal potential energyRadius of Al coreThermal evolution of 6 nm particle
NEEM MURINi-Coated Nano-Al Particles –Results (2/2)
• Adiabatic simulations to predict heat release due to inter-metallic reactions
Thermal evolution of 11 nm particle
• 10 nm Al core, 1 nm Ni shell (30 wt % Al) : solid Ni shell unable to withstand tensile stress
• Inter-metallic heat release → self-heating of particle;Inter metallic heat release self heating of particle; adiabatic reaction temperature of ~ 2150 K
• Low wt % of Al (3 nm Al core, 2 nm Ni shell) --insufficient Al atoms to exothermically react with Niinsufficient Al atoms to exothermically react with Ni → insignificant heat release
PhenomenonTemperature, K
Adiabatic simulation for 11 nm particle
Phenomenon 3 nm 6 nm 10 nm1 nm 2 nm 1 nm 2 nm 1 nm
Al core melting 800 800 990 990 1050
Ni-Al reactions 1370 – 1100 1580 1120
Reaction temperature 1900 – 2000 – 2150
NEEM MURI
Burning Characteristics of Nano Aluminum ParticlesBurning Characteristics of Nano Aluminum Particles in Flow Environments
i t t-- air -- steam -- water
NEEM MURI Flame Speed as Function of Particle Diameter in Mono-Dispersed Aluminum/Air Mixture
Kinetic-Controlled RegionKinetic-Controlled Region Diffusion-Controlled RegionDiffusion-Controlled Region
• For non-preoxidized particles, ti l t b l
• For non-preoxidized particles, ti l t b l
10-7 10-6 10-5 10-4
101
φ = 0.85
non-preoxidatedparticles
Kn > 1 Kn < 1particles at sub-nano scales are assumed to behave as large molecules. The maximum flame speed is achieved with particle size
particles at sub-nano scales are assumed to behave as large molecules. The maximum flame speed is achieved with particle size
s
100
d−0.59preoxidatedparticles
approaching to its molecular limit.
• For pre-oxidized particles, as the percentage of active aluminum and
approaching to its molecular limit.
• For pre-oxidized particles, as the percentage of active aluminum and
S L,m
/s10-1
Risha et al. [8]Boichuk et al. [6]Goroshin et al. [4]Goroshin et al. [3]B ll l [2] d−0 98
the energy content of the particle drop below a critical point, the flame speed of the particle-laden flow begins to decrease with
the energy content of the particle drop below a critical point, the flame speed of the particle-laden flow begins to decrease with
7 6 5 4
10-2Ballal [2]Cassel [1]Molecular limit (present)Theory (present)
d 0.98gdecreasing particle size. At the extreme situation, the energy release from particle oxidation may not even be able to sustain a flame
gdecreasing particle size. At the extreme situation, the energy release from particle oxidation may not even be able to sustain a flame
particle diameter, m10-7 10-6 10-5 10-4
0not even be able to sustain a flame. not even be able to sustain a flame.
NEEM MURICombustion of Nano-Aluminum and Liquid Water
Al-water zone
Mass conservation of mixture u L ign LS u Vρ = ρ = ρ
2
2 p,2 2 2
dT d TC u
dx dxρ = λ
Energy conservation
TvapTu
Al+ liquid water
Al +steam
Reaction zone
Post-flame zone
X= - ∞ X= - t
u
vap
x ,T T
x t, T T
→ −∞ →
= − =
Boundary conditionvap
• Analytical solution for preheat zoneX ∞ X t
Al-steam zone
2dT d TEnergy conservation
• Analytical solution for preheat zone • Thickness (t), flame speed unknown• Solution iterated until T-t=Tvap,H2O
1 p,1 1 2
dT d TC u
dx dxρ = λ
x 0, T T= =Boundary condition
Heat fluxbalance
Tign
• Volume and mass fractions based on experimental packing density . Large particles, lean mixture → thick paste
2
ign
1 2 fg t H O ( l )
t t
x 0, T T
dT dTx t, h V
dx dx+ −
= − λ λ + ρ=x= - t x=0
NEEM MURI Combustion of Nano-Aluminum and Liquid Water (Modeling Details and Results 2/3)
Reaction zone
dT dT
Particle consumption Boundary condition
d
dp=38 nm, Φ=1
0
1
03
dxdTdx
+
−
=
λλ
ad
p
dT 0dxT Td 0
=
=
→p0
b0
MdMudx
= −τ
p
p0
p
dx 0,
d
dx L
1
0
=
→
=
=
Mixture energy equation
dT d dT⎛ ⎞
Boundary conditionp0
x L,d
0→ =
ignx 0,T T= =
x= 0 x=L
• Ignition temperature and burning time from Huang
3 p3 3 FdT d dTuC QWdx dx dx
⎛ ⎞ρ = λ +⎜ ⎟⎝ ⎠
g
x L,dT 0dx
→ = P = 3.65 MPa, Φ=1
g p g get al., 2009
• Smaller particle → higher wt % of oxide → Lower flame temperaturep
• Reaction zone thinner at higher pressures & for smaller particles → smaller combustion time scales
NEEM MURI Combustion of Nano-Aluminum and Liquid Water (Modeling Details and Results 3/3)
P = 3.65 MPa, Φ=1 P = 3.65 MPa, dp=38 nm Φ=1, dp=38 nm
• Burning rates decrease significantly with particle size in spite of high flame temperatures
• Increase in flame speed with equivalence ratio
Φ=1, dp=38 nm
• Increase in flame speed with equivalence ratio attributed to increase in energy release rate
• Reduction of flame thickness with pressure due to quicker burnout of particles (kineticallyto quicker burnout of particles (kinetically controlled combustion)
NEEM MURIPublications
1. P. Puri, V. Yang, Effect of Particle Size on Melting of Aluminum at Nano Scales, Journal of Physical Chemistry C, Vol.111,2007, pp.11776-11783
2. P. Puri, V. Yang, Effect of Voids and Pressure on Melting of Nano-Particulate and Bulk Aluminum, Journal of NanoparticleResearch, Vol. 11 (5), 2009, pp.1117-1127( ) pp
3. Y. Huang, G.A. Risha, V. Yang, R.A. Yetter, Effect of Particle Size on Combustion of Aluminum Particle Dust in Air,Combustion and Flame, Vol.156, 2009, pp.5-13
4. Y. Huang, G.A. Risha, V. Yang, R.A.Yetter, Combustion of Bimodal Nano/Micro-Sized Aluminum Particle Dust in Air,Proceedings of the Combustion Institute, Vol. 31, 2007, pp. 2001-2009.
5. P. Puri, V. Yang, Pyrophoricity of Aluminum at Nano Scales, Combustion and Flame, In review, g, y p y , ,6. P. Puri, V. Yang, Thermo-mechanical Behavior of Nano Aluminum Particles with Oxide Layers During Melting, Journal of
Physical Chemistry, In review7. D.S. Sundaram, Y. Huang, P. Puri, G.A. Risha, R.A. Yetter, V. Yang, Flame Propagation of Nano-Aluminum-Water Mixture,
Combustion and Flame, In Preparation8. D.S. Sundaram, P. Puri, V. Yang, Thermo-Mechanical Behavior of Nickel-Coated Nano-Aluminum Particles, Journal of, , g, , f
Physical Chemistry, In Preparation9. P. Puri, D.S. Sundaram, V. Yang, Ignition and Combustion of Aluminum Particles at Micro and Nano Scales, Progress in
Energy and Combustion Science, In Preparation10. P. Puri, D.S. Sundaram, V. Yang, A Multi-Scale Theory on Ignition and Combustion of Aluminum Particles, Combustion and
Flame, In PreparationFlame, In Preparation11. P. Puri, V. Yang, Thermo-Mechanical Behavior of Nano Aluminum Particles with Oxide Layers, AIAA Paper 2008-93812. P. Puri, V. Yang, Molecular-Dynamics Simulations of Effect of Pressure and Void Size on Melting of Aluminum, AIAA Paper
2007-564413. P. Puri, V. Yang, Molecular Dynamics Study of Melting of Nano Aluminum Particles, AIAA Paper 2007-142914. Y. Huang, G. A. Risha, V. Yang, and R.A. Yetter, Flame Propagation in Bimodal Nano/Micro-Sized Aluminum Particle/Air14. Y. Huang, G. A. Risha, V. Yang, and R.A. Yetter, Flame Propagation in Bimodal Nano/Micro Sized Aluminum Particle/Air
Mixtures, AIAA Paper 2006-115515. G. A. Risha, Y. Huang, R. Yetter, and V. Yang, Combustion of Aluminum Particles with Steam and Liquid Water, AIAA Paper
2006-1154
NEEM MURI Acknowledgements
This work was sponsored by the U.S. Army Research Office under the M l i U i i R h I i i i d C N W911NF 04 1Multi-University Research Initiative under Contract No. W911NF-04-1-0178. The support and encouragement provided by Drs. Ralph Anthenien is gratefully acknowledged.
NEEM MURI
THANKS !
NEEM MURI Characteristic Time Scale Study(Effect of Temperature)
nm)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c> treacV1500 K, 1 atm
m)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c> treac
tmelt,c< tmelt,sII
V2000 K, 1 atm
xide
thic
knes
s(n
100
10tmelt,c< tmelt,s
tmelt,s< treac
I
IIIV
IV V
ide
thic
knes
s(nm
100
10 melt,c melt,s
tmelt,s< treac
I
IIIV
IV V
Core size (nm)
Ox
20 40 60 80 100
10-1 IIIVIVI
Core size (nm)
Oxi
20 40 60 80 100
10-1III
VIVI
ess(
nm)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c> treac
tmelt,c< tmelt,sII
IV V2500 K, 1 atm
ess(
nm)
101
tmelt,s=tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c> treac
tmelt,c< tmelt,s
IIIV
V3000 K, 1 atm
Oxi
deth
ickn
e
10-1
100
tmelt,s< treac
I
III
IV V
VIVI O
xide
thic
kne
10-1
100
tmelt,s< treac
I
III
IV V
VIVI
Core size (nm)20 40 60 80 100
10 VI
Core size (nm)20 40 60 80 100
10 VIVI
Nano Engineered Energetic Materials (NEEM)Vigor Yang, Georgia Institute of Technology
Objective: A comprehensive theory and predictive methodology for ignition & combustion of aluminum particles at different length scales
Scientific issues: Stage I (particle heating/phase transformations) Stage II (core melting and ignition due to melting/cracking)
• Thermo-mechanical behavior of nano aluminum particles with and without coatings at different length scales
Effect of particle size on ignition and combustion
Stage I (particle heating/phase transformations) Stage II (core melting and ignition due to melting/cracking)
Stage III (heterogeneous reactions/healing of cracks)
melting of oxide layer to form cap (Micro)
particle consumed due to heterogeneous reactions
(Nano)
• Effect of particle size on ignition and combustion characteristics of nano particulate aluminum
• Collective behavior of particles in energetic materials and flow environments Stage V (detached flame front (micro))
Major Accomplishments:
• Studied thermophysical behaviors of bulk and particulate aluminum with different coatings over a broad range of scales
Army Relevance: A comprehensive and quantitative knowledge of combustion and ignition of nano aluminum particles. The theoretical framework and computational methodology g
• Established a unified theory accommodating the various processes and mechanisms involved in the ignition & combustion of aluminum particles at micro and nano scales
developed can be applied to a variety of nano metal particulates.
Funding Profile: $100K per year
Grant # W911NF-04-1-0178• Examined the burning characteristics of aluminum
particles in flow environments
Graduate Students: Puneesh Puri, Dilip Sundaram
Grant # W911NF 04 1 0178
PI Contact information: Vigor Yang
Email: [email protected] Ph: 404-894-3002
NEEM MURI Ignition Criteria Two Different Thoughts
• Melting of aluminum core and ensuing volume expansion lead to pressure buildupvolume expansion lead to pressure buildup
• Due to low surface curvature of small particles, oxide layer is subject to higher tension as compared to large particles.p g p
• This causes rupture of the oxide shell and hence ignition.
20 30 h ti i t t 873 & 1173 K20 30 h ti i t t 873 & 1173 K
• Ignition criteria is determined by self heating, involving phase transformations and cracking in oxide shell.
• Ignition criteria is determined by self heating, involving phase transformations and cracking in oxide shell.
20-30 nm; heating air temperature: 873 & 1173 KRef: Rai et al., JPC, 200420-30 nm; heating air temperature: 873 & 1173 KRef: Rai et al., JPC, 2004
gg
• At micron scales, particles ignite at melting point of alumina with formation
• At micron scales, particles ignite at melting point of alumina with formation
Ignition temperature as function of particle diameter. Ref: Dreizin et al., C & F, 2005Ignition temperature as function of particle diameter. Ref: Dreizin et al., C & F, 2005
of an oxide cap.of an oxide cap.
NEEM MURI Shape Assumed by Nano-Particles due to Surface Tension
2 nm 3 nm 4 nm
6 nm5 nm 7 nm
Bulk8 nm 9 nm
NEEM MURICharge Development on Nano Particle
• Melting of nano-particle and bulk aluminum different on the basis of
• Melting of nano-particle and bulk aluminum different on the basis of charges
• Simulations performed using complete S-M potential with charge
l i (E b dd d
charges
• Simulations performed using complete S-M potential with charge
l i (E b dd devolution (Embedded atom + Electrostatic part of S-M potential) and Embedded atom potential (Embedded atom part of S-M
evolution (Embedded atom + Electrostatic part of S-M potential) and Embedded atom potential (Embedded atom part of S-M without charge evolutionpotential)
• Surface charge development on aluminum is too small in case of the
potential)
• Surface charge development on aluminum is too small in case of the S-M potential to make electrostatic forces substantial.
• Similar melting temperature from b th E b dd d t d S M
S-M potential to make electrostatic forces substantial.
• Similar melting temperature from b th E b dd d t d S Mboth Embedded-atom and S-M potential for a 3 nm particleboth Embedded-atom and S-M potential for a 3 nm particlewith charge evolution
NEEM MURIParticulate vs. Bulk Aluminum Melting
Melting simulation for bulk aluminum with periodic boundary conditions
Melting simulation for bulk aluminum with periodic boundary conditions
Melting simulation for aluminum in particulate phase
Melting simulation for aluminum in particulate phase
NEEM MURI Effect of Oxide Thickness and Core Size
5 nm (diameter) Al core + 2 nm thick Al2O3 (9 nm particle)
9 nm (diameter) Al core + 3 nm thick Al2O3 (15 nm particle)
NEEM MURI Summary and Conclusions
The bulk melting is characterized by a sharp increase in structural and thermodynamic properties, whereas the particulate phase involves surface pre-melting. p p , p p p gA perfect crystal with periodic boundary conditions is associated with structural melting which predicts the melting point greater than the thermodynamic melting point. Structural melting occurs at 1244 K. From the study of bulk crystals with 864 and 2048 atoms, it was concluded that the ratio y y ,between the structural and thermodynamic melting points for aluminum is 1.32. The range of critical void size increases as the number atoms considered to represent the bulk phase increases (1.7 and 5.0 nm3 for 864 and 2048 atoms, respectively). Irrespective of particle size, the effect of defect nucleated melting is negligible in case ofIrrespective of particle size, the effect of defect nucleated melting is negligible in case of nanoparticles because of the presence of surface which acts as nucleation site. It can be concluded that the primary mechanism of melting is nucleation at a surface or void. Phenomena like generation of dislocation were observed in the current study, but theirPhenomena like generation of dislocation were observed in the current study, but their impact is negligible as compared to nucleation which is the main mechanism of melting. Melting temperature is independent of shape and type of void which is fully consistent with previous studies. The effect of pressure on the defect nucleated melting of aluminum has also beenThe effect of pressure on the defect nucleated melting of aluminum has also been investigated and is negligible for pressures up to 300 atm.
NEEM MURI Modeling of Bimodal Aluminum Dust Flame at Fuel-Lean Conditions
preheat flame post flameflame flame
a) overlapping flame
preheat flame post flameflame
b) separated flame
preheatzone zone III zone
Tparticles heatedby local gas
gas heated byburning of
l i l
zone I zone II
,2ignT
preheatzone I
flamezone II
post flamezone
Tparticles heatedby local gas
burning of
flame zone I
,2ignT
preheatzone II
x
,1ignTgas heated byconduction fromflame zone
large particles
burning ofsmall particles
overlappingburning
gas heated byconduction fromflame zone
x
,1ignTbu g o
large particles
burning ofll ti l
,1bx v= τ
x0x =
small particles0x Z= 0 ,2bx Z v= + τ
,1bx v= τ
x
0x =small particles
0x Z= 0 ,2bx Z v= + τ
• Flame configuration depends on the mass concentration, particle size, ignition • Flame configuration depends on the mass concentration, particle size, ignition g p , p , gtemperature, and burning time of each group of aluminum particles.
• Ignition temperature and burning time of aluminum particle are needed as input parameters
g p , p , gtemperature, and burning time of each group of aluminum particles.
• Ignition temperature and burning time of aluminum particle are needed as input parametersparameters. parameters.
NEEM MURI Laminar Flames of Mono- and Bimodal-Dispersed Aluminum Particles/Air Mixtures
100% micro particles (5–8 μm)100% micro particles (5–8 μm) 20% nano particles (100 nm) addition20% nano particles (100 nm) addition
Bimodal particle flame features increased flame speed and thicker flame zone. Bimodal particle flame features increased flame speed and thicker flame zone.
NEEM MURI Characteristic Time Scale Study (II)
t l =t l
tmelt,c> treac V1000 K, 1 atm
O Anions
Al Cations
O Anions
Al Cations
O Anions
Al Cations
ss(n
m)
101
tmelt,s tmelt,ctmelt,c=treactmelt,s=treac
tmelt,c< tmelt,sIIIV
Phase TransformationsPhase TransformationsPhase Transformations
eth
ickn
es
100
, ,
IIV VO2 Molecules
Oxi
de
10-1
tmelt,s< treac
IIIVIVI
Core size (nm)20 40 60 80 100
Oxide cap
Al (g)
oxidizer
Oxide cap
Al (g)
oxidizer
Detached Flame front
Oxide cap
Detached Flame front
Oxide cap