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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
THE EFFECT OF ADDED AL2O3 ON THE PROPAGATION BEHAVIOR W911NF-04-1-0178
OF AN Al/CuO NANOSCALE THERMITE
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
J. Y. Malchi a, Richard A. Yetter a,*, T. J. Foley b, and Steven F. Son c
5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
REPORT NUMBER
a The Pennsylvania State University, University Park, PA, USA
b Los Alamos National Laboratory, Los Alamos, NM, USA
c Purdue University, West Lafayette, IN, USA
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)
U. S. Army Research Office
P.O. Box 12211
Research Triangle Park, NC 27709-2211 11. SPONSOR/MONITOR'S REPORT
NUMBER(S)
12. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release; federal purpose rights.
13. SUPPLEMENTARY NOTES
The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official
1T4h.e A vBiSewTRsA, oCpTi nions and/or findings contained in this report are those of the author(s) and should not be construed as an official
DTherpeaer ttmypeenst ooff ethxep eArrimmeyn ptso switeiroen ,p perofloicrmy eodr doenc aisni oAnl,/ CunulOes sn asnoo dsecsailgen tahteerdm biyte ottoh uern ddeorcsutamnedn tthaeti oenff.ect of adding a diluent (40 nm
Al2O3 particles) to the mixture: the constant volume pressure cell, the unconfined burn tray, and the instrumented burn tube. The
addition of Al2O3 decreased the pressure output and reaction velocity in all three experiments. Burn tube measurements showed
three reaction velocity regimes: constant velocity observed when 0% (633 m/s) and 5% (570 m/s) of the total weight is Al2O3,
constant acceleration observed at 10% (146 m/s to 544 m/s over a distance of 6 cm) and 15% (69 m/s to 112 m/s over a distance of 6
cm) Al2O3, and an unstable, spiraling combustion wave at 20%Al2O3. The pressure measurements correlated to these three regimes
showing a dropoff in peak pressure as Al2O3 was added to the system, with relatively no pressure increase observed when 20% of
the total weight was Al2O3. Equilibrium calculations showed that the addition of Al2O3 to an Al/CuO mixture lowered the flame
temperature, reducing the amount of combustion products in the gas phase, thus, hindering the presumed primary mode of forward
heat transfer, convection.
15. SUBJECT TERMS
Burning rate; Diluent; Nano-aluminum; Thermite
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON
a. REPORT b. ABSTRACT c. THIS PAGE ABSTRACT OF Richard A. Yetter
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The Effect of Added Al O on the Propagation Behavior of an Al/CuO
2 3
Nanoscale Thermite
J. Y. Malchi a; R. A. Yetter a; T. J. Foley b; S. F. Son c
a The Pennsylvania State University, University Park, PA, USA b Los Alamos National Laboratory, Los
Alamos, NM, USA c Purdue University, West Lafayette, IN, USA
Online Publication Date: 01 July 2008
To cite this Article Malchi, J. Y., Yetter, R. A., Foley, T. J. and Son, S. F.(2008)'The Effect of Added AlO on the Propagation Behavior
2 3
of an Al/CuO Nanoscale Thermite',Combustion Science and Technology,180:7,1278 — 1294
To link to this Article: DOI: 10.1080/00102200802049471
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Combust.Sci.andTech.,180:1278–1294,2008
Copyright#Taylor&FrancisGroup,LLC
ISSN:0010-2202print/1563-521Xonline
DOI:10.1080/00102200802049471
THE EFFECT OF ADDED AL O ON THE PROPAGATION
2 3
BEHAVIOR OF AN Al/CuO NANOSCALE THERMITE
J. Y. Malchi1, R. A. Yetter1, T. J. Foley2, and S. F. Son3
1ThePennsylvaniaState University, University Park, PA,USA
2LosAlamos NationalLaboratory, LosAlamos, NM, USA
3PurdueUniversity, West Lafayette, IN,USA
9
0
0 ThreetypesofexperimentswereperformedonanAl/CuOnanoscalethermitetounderstand
2
il theeffectofaddingadiluent(40nmAl2O3particles)tothemixture:theconstantvolume
pr pressure cell, the unconfined burn tray, and the instrumented burn tube. The addition of
A
15 Al2O3decreasedthepressureoutputandreactionvelocityinallthreeexperiments.Burn
tubemeasurementsshowedthreereactionvelocityregimes:constantvelocityobservedwhen
2
9:4 0%(633m/s)and5%(570m/s)ofthetotalweightisAl2O3,constantaccelerationobserved
1 at10%(146m/sto544m/soveradistanceof6cm)and15%(69m/sto112m/soveradis-
:
At tanceof6cm)Al2O3,andanunstable,spiralingcombustionwaveat20%Al2O3.Thepress-
] uremeasurementscorrelatedtothesethreeregimesshowingadropoffinpeakpressureas
y
t
i Al O wasaddedtothesystem,withrelativelynopressureincreaseobservedwhen20%of
s 2 3
ver thetotalweightwasAl2O3.EquilibriumcalculationsshowedthattheadditionofAl2O3to
ni anAl/CuOmixtureloweredtheflametemperature,reducingtheamountofcombustionpro-
U
e ductsinthegasphase,thus,hinderingthepresumedprimarymodeofforwardheattransfer,
t
a convection.
t
S
a
i
an Keywords: Burningrate;Diluent;Nano-aluminum;Thermite
v
l
y
s
n
n
e
P
[
y: INTRODUCTION
B
d
de Athermitereactionisdefinedasareactionbetweenametalandametaloxide
a
o
l (Wang et al., 1993). This work was focused on the metal-metal oxide reaction, not
n
w
Do intermetallics (another name for metal-metal reactions). Using aluminum as the
metal fuel with different oxidizers creates highly exothermic reactions that have
applications in many areas associated with self-propagating high temperature
Received16January2007;acceped19December2007.
AuthorsaresupportedbyLosAlamosNationalLaboratory(LANL),whichisoperatedforthe
U.S.DepartmentofEnergyunderthecontractDE-AC52-06NA25396.WorkwassupportedbytheJoint
DoD=DOE Munitions Program under the supervision of Sherri Bingert and the U.S. Army Research
Office under the Multi-University Research Initiative under Contract No. W911NF-04-1-0178. The
authorsgiveaspecialthankyoutoAdamPachecoandDaveOschwaldfortheirhelpsettingupandrun-
ningtheequipmentthatmadethisstudypossible.Forhishelpinterpretingpressuretransducerresults,Dr.
Patrick Walter of Texas Christian University is thanked as well. This work has been assigned LA-UR
#07-7888.
Address correspondence to R. A. Yetter, 111 Research Bldg. East, University Park, PA 16802.
E-mail:[email protected]
1278
PROPAGATIONBEHAVIOROFAl=CuONANOSCALETHERMITE 1279
synthesis (SHS) (Wang et al., 1993) and energetic materials (Naud et al., 2003;
Pantoya et al., 2004).
Burningvelocitiesforthesematerialshavebeenshowntobehighlydependent
on the particle size (Pantoya and Granier, 2005), whereby smaller particles lead to
faster burning rates. Thermites with particle sizes on the nanoscale, also referred
to as metastable interstitial composites (MICs), can exhibit burning rates up to
1000m=s (Bockmon et al., 2005). The high burning rates and exothermicity makes
these materials of great interest to the combustion community.
OneaspectofMICmaterialsthatisnotwellunderstoodisthemodebywhich
energy is transferred ahead of the reaction front to sustain the propagation, or the
propagation mechanism. Five propagation mechanisms may be considered when
examining the reaction propagation: radiation, conduction, acoustics, compaction,
and convection (Asay et al., 2004). Solid energetic materials are controlled by con-
duction,whendeflagrating,whichcanbeenhancedbyradiation(SonandBrewster,
9
0
20 1995; Begley and Brewster, 2007). Acoustics (shock processes) and compaction
il become important when a reaction produces pressures sufficient to induce volume
r
p
A changes in the material. This occurs during detonation or the transition to deton-
5
1 ation. Convection is possible if the material is porous and hot interstitial gas, reac-
2
:4 tants, or products can be propelled forward through the material by high reaction
9
1
zone pressures (Kuo et al., 1978; Ershov et al., 2001).
:
t
A Nanoscale thermites exhibit combustion velocities ((cid:1)1000m=s) approxi-
]
ty mately four orders of magnitude greater than that of the micron-scale thermites
i
s
r ((cid:1)0.1m=s) (Bockmon et al., 2005 and Wang et al., 1993). The drastic increase
e
v
ni in velocity is due to the extremely small time scales associated with mass diffusion
U
e and reaction rates brought about by the small particle sizes. This does not allow
t
a
t time for any heat loss or depressurization within the reaction zone leading to high
S
ia pressure, hot gases that can be propelled ahead of the front. Therefore, these sys-
n
va tems are thought to be controlled by a convective propagation mechanism (Asay
l
y
s et al., 2004).
n
n
Pe Because the controlling propagation mechanism is convection, both gas pro-
[
: ductionandtemperature, shouldbeimportant factorswhen optimizingforthefast-
y
B
est burning rate. Sanders et al. (2006) observed that for four different metal oxides
d
e
oad (Bi2O3, MoO3, CuO, and WO3), the burning rate on a burn tray was maximized
nl atthestoichiometrythatalsoproducedthehighestpeakpressureinthepressurecell.
w
Do Moreover, equilibrium calculations showed that all of the optimum stoichiometric
ratios were related to the gas production and phase of the products. This optimum
stoichiometrywasfoundtobefuelrich((cid:1)1.4)forallofthemetaloxidesexceptcop-
per oxide, which optimized at an equivalence ratio close to 1. This difference was
attributed to the fact that one of the main products, copper, has a relatively high
boilingpointof2835Kandneededthehightemperatureofastoichiometricreaction
to keep it in the gas phase. This work focused on the reaction of nano-aluminum
(nAl) with copper oxide. The global reaction is
2Alþ3CuO!Al O þ3Cu DH ¼(cid:2)4:08 kJ=g ð1Þ
2 3 r
where DH is the heat of reaction based on the mass of the reactants.
r
1280 J.Y.MALCHIETAL.
Similar to varying the stoichiometry, adding a diluent into the system will
decrease the overall temperature of the reaction. Adding the end product, parti-
cularly Al O , as a diluent was a common practice in micron-scale thermite SHS
2 3
in order to reduce combustion temperatures and change the mechanical properties
of the products (Varma et al., 1992; Munir and Anselmi-Tamburini, 1989). More-
over,thedecreaseincombustiontemperaturegavewaytoslower reactionvelocities
and decreasing amounts of gaseous species (Wang et al., 1993).
This work focused on the effects of dilution on the combustion properties of
the Al=CuO nano-scale thermite. Alumina nano-particles were added in given per-
centages and their effect on pressure and reaction velocity was studied. A similar
study was performed with an Al=MoO system by Foley et al. (2006) from which
3
comparisons are made. The global reaction for this thermite system is given in
Eq. (2).
9
0
0 2AlþMoO !Al O þMo DH ¼(cid:2)4:70 kJ=g ð2Þ
2 3 2 3 r
l
i
r
Ap The authors hypothesized that the dilution will lower combustion temperatures,
15 which will decrease gas production and, thus hinder the convective propagation
2
4 mechanism.
:
9
1
:
t
A
] EXPERIMENT
y
t
i
rs Threeexperimentswereperformedtocharacterizetheeffectsofaddingadilu-
e
v
i ent (Al O nano-particles) to an Al=CuO nanoscale thermite or MIC. The pressure
Un 2 3
e cell gave pressure traces for a constant volume explosion, the burn tray yielded a
t
ta two-point velocity of the reaction propagating through the unconfined material,
S
a and the burn tube provided information about the pressure and reaction velocity
i
n
va in confined conditions. Brief descriptions are given here, but detailed experimental
l
sy descriptions can be found in Sanders et al. (2006).
n
n
e
P
[
:
By Materials and Material Preparation
d
e
ad Note: Care should be exercised and small amounts of material used when
o
nl handling the formulated composites because of their sensitivity to impact, spark,
w
o
D and friction.
Nano-aluminum was purchased from Nanotechnologies Inc. (currently, Nova-
centrix Inc.) and had a nominal particle size of 80nm with 88% active aluminum
(Mangetal.,2006).Particleswereassumedtoallhaveasphericalgeometry.Copper
oxide particles were purchased from Technologies Inc. with all particles assumed to
havecylindricalgeometrywithdimensionsof21nm (cid:3) 100nm.Assumptionsonpar-
ticle geometries are from SEM analysis of the Al and CuO particles (Fig. 1). The
alpha-aluminum oxide (Al O ) particles were purchased from Nanotechnologies
2 3
Inc. and had a nominal particle size of 40nm.
All composites had aratio of22% nAl and78%CuO bymass which isbased
ontheoptimizationfromSandersetal.(2006).Aluminawasaddedtothissystemin
increments to produce the desired dilution (increments are labeled as percentage of
addedalumina,thustheoverallaluminapercentagewillbehigherduetotheinherent
PROPAGATIONBEHAVIOROFAl=CuONANOSCALETHERMITE 1281
9
0
0
2 Figure1 SEMofAl=CuOnanoscalethermiteat25K(cid:3)magnification.
l
i
r
p
A
15 alumina shell on the nAl). Mixtures were combined in glass vials and slurried in
42 (cid:1)12mlofhexanes.Theslurrywassonicatedforatotalof1minutein0.5sintervals
:
19 (50% duty-cycle) at 200W using a Heat Systems XL 2020 sonicator. It was then
At: placed in a steel pan and dried on a hot plate at (cid:1)48(cid:4)C for (cid:1)10 minutes (until
y] material appeared dry). The material was then sieved through a 355mm mesh to
t
si break up any large agglomerates.
r
e
v
i
n
U
te Pressure Cell
a
t
S
a A modified Parr bomb was used to acquire constant volume pressure traces
i
n
a (Perry et al., 2004). Ignition was achieved by pulsing a 1064nm Nd:YAG laser
v
l
sy ((cid:1)9mJ)ontothematerialinthecellviaanopticalfiber.Thefreevolumeofthecell
n
en was13cm3andtheappropriateamountofmaterialwasplacedinacuprestingatthe
P
[
bottom of the cell. Pressure measurements were taken at the wall of the cell using a
:
y
B PCB Piezotronics piezoelectronic pressure transducer with a PCB Piezotronics
d
de signal-conditioner (model 482A20). Data were recorded at 10MHz with a National
a
o
l Instruments PCI-6115 data acquisition board (DAQ). The q-switch from the laser
n
w
Do was used to trigger the data acquisition system.
The mass of MIC material placed in the cup remained a constant value of
17.5mgirrespectiveoftheamountofaddeddiluentinthesystemtokeeptheenergy
content constant. For example, if an experiment was being performed on a sample
with 5% added Al O nano-particles, the amount of MIC would be 17.5mg (22%
2 3
by mass nAl including oxide passivation, and 78% CuO), but the total mass of
material in the cup would be 18.42mg.
Burn Tray
Aloosesampleofmaterial(50mg)waslineduponametaltraytomeasurean
unconfined reaction velocity (Perry et al., 2004). Two holes, (cid:1)1mm in diameter,
were 20mm apart on the base of the metal tray, on top of which the material was
1282 J.Y.MALCHIETAL.
placed.Twoopticalfiberswereplacedintheseholesandattachedontheirotherend
to aThorlabs DET-210photodiodeto detect light emission from thereaction atthe
beginning and end of the line of material. The distance and time between these two
light signals were used to find a two-point velocity. The light from the first photo-
diode was also used as a trigger for the DAQ system. The data were collected by
the same DAQ system described in the previous section. Material ignition was
achieved by piezoelectric discharge.
Burn Tube
The burn tube experiment originally designed and used by Bockmon et al.
(2005) was used in this experiment with some modifications. This experiment gave
ameansofmeasuringthereactionvelocityinaconfined,moreone-dimensional,cyl-
indrical geometry. An acrylic tube used to hold the material, with length of 8.9cm,
9
0
20 innerdiameterof0.32cm,andouterdiameterof0.64cm,wasplacedinapolycarbo-
il nateblock.Sixpressuretransducersandopticalfiberportswerelocatedoneachside
r
p
A of the block at 1cm intervals.
5
1 Materials were loaded into acrylic tubes using a Cleveland vibrating block to
2
:4 assure uniform powder density. Packing densities were approximately 6% of the
9
1
theoreticalmaximumdensity(TMD),whichcorrespondedto250mgperexperiment
:
At or 0.36g=cm3. Initiation of the reaction was achieved by means of an exploding
]
ty bridge wire (EBW), which was placed at one end of the tube and fired by a Cordin
i
s
r 640 Pulsor at 1.7kV. A Stanford Research Systems pulse generator was used to
e
v
ni manually trigger the Pulsar and DAQ system. The signal from the pulse generator
U
e correspondstot¼0intheexperiments.FortheseexperimentstwoTektronixdigital
t
a
t oscilloscopes (models 754D and 7054) with sampling rates of 5MHz (0.2ms resol-
S
ia ution) were used to acquire the data.
n
va APhantom7.0high-speedvideocamerawasusedtoviewtheluminosityfrom
l
y
s the reaction wave propagating down the tube. A frame rate of 110,000 frames per
n
n
Pe second was used at a pixel resolution of 256(cid:3)32 and exposure time of 1ms. An
[
: appropriate aperture was chosen depending on the experiment to view the reaction
y
B
without saturation. The pulse generator triggered the camera as well.
d
e
d
a
o
l
n
w RESULTS
o
D
Three tests were performed to characterize the effects of added Al O nano-
2 3
particles on the burning rate of an Al=CuO nanoscale thermite: the pressure cell,
theburntray,andtheburntube.Boththepressurecellandtheburntraygaveinfor-
mationaboutanunconfinedburnwhiletheburntubewasinaconfinedsetup.Con-
finementeffectswereexpectedtoplayasignificantrolebecausetheconvectivemode
of heat transfer was the controlling propagation mechanism.
Pressure Cell and Burn Tray
A single pressure trace was recorded in the pressure cell for each experiment.
Typical results are shown in Figure 2 for varying weight percent of Al O . Below
2 3
5%addedAl O ,ringingwasseenintherecord.Thiswasinterpretedasshockwaves
2 3
PROPAGATIONBEHAVIOROFAl=CuONANOSCALETHERMITE 1283
9
0
0
2
l
i
r
p
A
5
1
2
4
:
9
1
:
t Figure2 TypicalpressuretracesfromthepressurecellforincreasingamountsofAlO.Datalabelsshown
A 2 3
] onlyoninitialpressureriseforeachtrace.
y
t
i
s
r
e
v
ni reflectingoffthewallsinsidethecell.Adrasticchangeoccurredinthepressuretraces
U
te when 5% Al2O3 was added to the mixture whereby the peak pressure and rate of
a
t pressure rise (dP=dt) significantly decreased and the induction time (s) significantly
S i
ia increased.
n
va The rate of pressure rise was defined asthe differencebetween the peak press-
l
y
s ure and atmospheric pressure divided by the difference between the time of peak
n
n
Pe pressure and the time where the pressure first rises above atmospheric conditions.
[
: Inductiontimewas definedasthetimefrom when theignitionenergywasdelivered
y
B
to when the pressure rises above 10% of the peak pressure. Moreover, above 5%
d
e
oad added Al2O3 there was no ringing in the pressure trace indicating the reaction was
nl slowed to the point that a shock wave was not produced in the gas surrounding
w
o
D the sample.
The Al=MoO system used in Foley et al. (2006) showed a similar drastic
3
change in behavior for the rate of pressure rise and induction time at 20% added
Al O (compared to 5% for the Al=CuO system), which indicated that the Al=CuO
2 3
CuO system was more sensitive to the addition of Al O . The peak pressure for the
2 3
Al=MoO system using 19mg, however, was relatively low (0.33MPa) compared to
3
theAl=CuOsystem(1.17MPa)forthesharprisingpressuretraces(lowpercentageof
Al O ).
2 3
ThepressuretraceswerefairlyrepeatableforeachAl=CuO=Al O case,except
2 3
forthe4%caseindicatingthesystemwasonthethresholdofachange.The4%case
was not shown due to its extremely high variability in results. Specifically, some
results in this range showed a sharp pressure rise with ringing and some resulted
in a more monotonic rise in pressure similar to conditions where more Al O was
2 3
1284 J.Y.MALCHIETAL.
9
0
0
2
l
i
r
p
A
15 Figure3 RateofpressureriseinthepressurecellwithincreasingweightpercentagesofAl2O3.
2
4
:
9
1 added. This distinct transition was indicative of a change in the mode of reaction
:
t
A propagation occurring.
]
ity Three experiments were performed for each weight percentage of Al2O3 in the
ers pressurecellandvaluesofpeakpressure,dP=dtandsiwereaveraged.Figures3and
v
i 4 show the trends of dP=dt and s, respectively. The slope of the pressure rise
n i
U
te dropped two orders of magnitude when the Al2O3 weight percentage increased
ta from 3% to 5%, showing two different regimes. The induction time also showed a
S
a
i
n
a
v
l
y
s
n
n
e
P
[
:
y
B
d
e
d
a
o
l
n
w
o
D
Figure4 Inductiontime(s)forthepressureriseinthepressurecellwithincreasingweightpercentageof
i
AlO.
2 3
PROPAGATIONBEHAVIOROFAl=CuONANOSCALETHERMITE 1285
9
0
0
2
l
i
r
p
A
5 Figure5 PeakpressureinParrbombandopentrayvelocityresult.Thereisaclearcorrelationbetween
1
peakpressureinthepressurecellandtwo-pointvelocityontheburntraywithincreasingweightpercen-
2
9:4 tagesofAl2O3.
1
:
t
A
] bimodalnaturewithasignificantincreaseat5%.Errorbarsrepresentinga95%con-
y
t
si fidenceintervalarepresentforallpoints,althoughsomearehiddenbytheirrespect-
r
ve ive label.
i
n
U Thetrendforthepeakpressure,whenvaryingtheweightpercentofAl O ,was
2 3
e
at similar to that for the two-point velocity in the burn tray experiment as shown in
t
S Figure 5. For both, there was an initial drop of (cid:1)27% in either peak pressure or
a
i
n velocity with only 1% Al O added and then a drastic dropoff of (cid:1)75% at 5%
a 2 3
v
syl Al2O3. In contrast, Foley et al. (2006) observed a linear decrease in peak pressure
enn and a change of regimes for velocity at 20% Al2O3 (Al=MoO3 system). Error bars
[P representing a 95% confidence interval are present, but smaller than the data point
:
y labels.ThecorrelationbetweenthepressureandvelocitywasalsoshowninSanders
B
ed et al. (2006) for various stoichiometric ratios. This gave further evidence that the
d
oa propagation mechanism was closely related to the effects of pressure or gas
l
n
w production.
o
D
TherewasalimittotheamountofAl O thatcouldbeaddedtothesystemfor
2 3
each test. The material in the pressure cell would not ignite with 15% by weight of
Al O by laser, nor in the burn tray with 20% Al O using a piezo-igniter. In con-
2 3 2 3
trast,theAl=MoO fromFoleyetal.(2006)wasignitablewith50%Al O usingthe
3 2 3
same ignition systems. The burn tray experiment had a higher threshold for Al O
2 3
becausetheignitionsystemsweredifferentandmorematerialwasusedandlesswas
incontactwithitscontainerpromotingmoreheatgenerationandlessheatlosses.
Burn Tube
As was shown with the pressure cell and burn tray, this material was parti-
cularly sensitive to the addition of Al O . An addition of only 5% by weight of
2 3
