Paper # 070HE-0162 Topic: Heterogeneous Combustion, Sprays & Droplets

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8th U. S. National Combustion Meeting Organized by the Western States Section of the Combustion Institute

and hosted by the University of Utah May 19-22, 2013

The Ignition and Combustion Study of Nano-Al and Iodine Pentoxide Thermite

Guoqiang Jian, Snehaunshu Chowdhury, Jingyu Feng and Michael R. Zachariah

Departments of Mechanical Engineering and Chemistry, University of Maryland, College Park,

Maryland 20742, United States Abstract

Thermite reactions with high energy release and biocidal agents’ production are of interest for their potential applications in bio-agent defeat. In this work, we investigated the ignition and combustion of nano-Al/micro-I2O5 thermite, and studied its potential use in biocidal applications. Cyro-milling technique was used to produce micro-sized I2O5 (~2-4 μm) which were used as the oxidizer in this study. The ignition and reaction of the prepared nano-Al/micro-I2O5 thermite were systematically studied by a rapid fine wire heating technique using a high speed digital camera and a temperature-jump/time-of-flight (T-Jump/TOF) mass spectrometer. The ignition temperature of nano-Al/micro-I2O5 thermite in air at atmospheric pressure was found to be ~810 K, lower than ignition temperature ~940 K in vacuum. Time-resolved mass spectra results confirmed that nano-Al/micro-I2O5 thermite reaction can produce a lot of iodine species which were suggested to be good biocidal agents. Thermal decomposition of the I2O5 oxidizer under rapid heating conditions were investigated by T-Jump/TOF mass spectrometer, and was found to release significant O2 before its thermite ignition. Constant-volume combustion cell tests were carried out to characterize the pressure rise and optical emissions during the thermite combustion events, and the performance of the I2O5 containing thermites was compared with other metal oxides thermite systems. The results show that Al/I2O5 thermite composite outperform the traditional Al/CuO and Al/Fe2O3 thermite systems in terms of peak pressure, pressurization rate and burning time. Additionally, we observed the concurrent pressure and optical rising for all nano-Al/micro-oxidizer thermites in this study. The results indicate that the pressure rise in nano-Al/micro-I2O5 thermite reaction should be from the produced hot biocidal species by very exothermic thermite reactions other than from the decomposition of oxidizers, suggesting the beneficial of using microsized I2O5 as the biocidal oxidizer. Transmission electron microscope with X-ray compositional microanalysis characterization was performed to analyze the post-combustion products and the production of iodine and aluminum oxides were found as main products. Additional studies of hygroscopic properties of I2O5 on its thermite reaction will also be discussed. Our study of Al/I2O5 thermites show that these I2O5 containing thermite reactions are very reactive and suggested to effectively produce iodine gas which can be used in microbial agent defeat applications.

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1. Introduction

Global terrorist threats involving the usage of biological agents highlight the need for preemptive neutralization of biological agent munitions, stockpiles and production facilities. The approaches for effective destruction of biological agents are being considered and an ideal neutralization of biological agents is suggested to possess both a thermal and long-lasting biocidal agent release. [1] Recently, one class of thermite reactions which exhibit both thermal and chemical defeat characteristics was proposed to be a promising approach to effectively neutralize this threat. [1-6]

The thermite reaction is a highly exothermic reaction between a metal fuel and metal oxide

oxidizer. Aluminum is most often the choice of fuel, due to its high reaction enthalpy, high thermal conductivity and availability. [7-8] A variety of oxidizers have been used in formulation of thermites, with the most studied oxidizers including Fe2O3, CuO, MoO3, Bi2O3, WO3, etc. [9-12] On the other hand, other oxidizers, such as KMnO4, [13] KClO4, [14] AgIO3, [1] are found to be highly reactive. Among these oxidizers, AgIO3 has been considered as a potential biocide due to the high thermal release and the reaction products. Sullivan et al. found that both silver and iodine species, which are known biocides, produced in the Al/AgIO3 thermite reactions were predominantly found in the exterior of the product particle, and thus were bio-available. [1] Another class of oxidizers containing iodine, such as I2O5 et al., [3, 6, 15] have been suggested, as a means to release significant quantities of gas phase iodine. Martirosyan et al. found that Al/I2O5 nanothermite produced much higher transient pressure pulse than traditional metal oxides based nanothermites. [6, 16] Clark and Pantoya tested the biocidal effects of different thermites reactions (Al+I2O5, Al+Ag2O, and Al+Fe2O3) on spore neutralization, and found that only the iodine containing thermite demonstrated significant spore neutralization. [3]

In this paper, we aim to further explore the Al/I2O5 thermite reaction. In particular, ignition and combustion performance along with the final state of the products will be studied. The ignition and reaction process of nano-Al/micro-I2O5 were characterized by a high speed digital camera and a temperature-jump/time-of-flight mass spectrometer (T-Jump/TOFMS) and whereby thermite reactions can be initiated from a rapidly heated fine wire. The decomposition of iodine pentoxide during rapid heating was also characterized by T-Jump/TOFMS. Constant-volume combustion tests were performed and compared with traditional thermites formulations. The post combustion products were characterized using transmission electron microscopy and X-ray analysis. The results demonstrate that the iodine containing thermites can produce a lot of iodine species and possess a good combustion performance, indicating their potential applications in biocide and energetic gas generators. 2. Methods

2.1. Sample preparation

The nano-aluminum samples used in this study were purchased from the Argonide Corporation, and designated as “50 nm ALEX”. The active aluminum was measured by TGA to be 70% by weight, and was considered when preparing the stoichiometric samples. Iodine pentoxide powder (I2O5) was purchased from Sigma-Aldrich (99.99 % purity) and stored in a glove box to prevent water adsorption. Powder X-ray diffraction (XRD, Bruker D8 Advance using Cu Kα radiation) results in Figure 1 show that the as received I2O5 contains small amount of HI3O8 which either from

manufacwere prprevent

Figurean

The m

microsc4 μm afMicrosiSigma-Acompos

cturing procepared by mwater uptak

e 1. XRD pand HI3O8. N

milled I2O5

copy (SEM, fter milling zed Fe2O3 aAldrich, andites compris

Figu

cess or watmechanical mke.

attern of as rNote: All oth

samples, aHitachi SU, as shown iand CuO pod summarizsed of nano

ure 2. SEM

er adsorptiomilling 1 ho

received I2Oher peaks w

as well as aU-70 FEG-S

in Figure 2.owders (<5

zed in Tablesize fuel an

M images of

3

on during Xour (Cyrom

O5 from Sigmithout mark

as-received EM), and th. The milled μm as spee 1. For thed microsize

as received

XRD characmill, Retsch)

ma-Aldrich ks in as recei

I2O5 were he images shd I2O5 particcified) used

ese thermitee oxidizers.

(a) and mill

cterization. Mof the as-re

and standarived I2O5 ar

characterizhow the parcles were usd in this stue formulatio

led (b) I2O

5

Microsized eceived I2O5

rd XRD patre from I2O5

zed by scanrticle sizes gsed in the foudy were puons, we can

particles.

I2O5 sampl5 in hexane

tterns of I2O5 phase.

nning electrgo down to ollowing tesurchased fro

take them

les to

O5

ron 2-

sts. om as

4

Thermite samples were prepared by mixing of nano-aluminum and I2O5 powder in stoichiometric ratio. The mixed samples were ultrasonicated in ~10 ml hexane for about 30 min to ensure the mixing between the fuel and oxidizer. For the wire heating experiments, the prepared sample suspension was coated onto a ~10 mm long, 76 µm diameter platinum wire with a micropipette. For the constant volume combustion cell tests, the ultrasonicated thermites sample suspension were kept in a vacuum oven at 333 K (60 oC) to allow the hexane to fully evaporate. The dry powder was then gently broken apart to a loose powder. 2.2.Time-resolved mass spectrometry measurement and wire ignition with high speed imaging

The recently developed temperature-jump/time-of-flight mass spectrometer (T-Jump/TOFMS) [17] was used to characterize the decomposition of I2O5 and the thermite reaction between nano-Al and I2O5. The T-Jump probe (76 µm Pt wire) is directly inserted close to the electron ionization (EI) region of the TOF mass spectrometer, which enables continuously monitoring of a reaction event with a temporal resolution of 100 µs per mass spectrum. Typically, the T-Jump filament (Pt wire, length ~12 mm, diameter ~76 µm) was coated with a thin layer of sample powder (~0.1 mg) and directly inserted close to the electron ionization (EI) region of the mass spectrometer. The coated Pt wire can be rapidly joule heated up to ca. 1800 K in 3 ms, corresponding to a heating rate of ~5×105 K/s. The Pt wire was replaced after each heating event. From the voltage and current trace, a resistivity measurement can be obtained and related to the instantaneous temperature of the Pt wire, which can be mapped against the time resolved mass spectra. Time-resolved mass spectra combined with temperature profile were then used for characterization of decomposition or thermite reaction. A detailed experimental description of T-Jump/TOFMS can be found in our previous papers. [17, 18]

High speed imaging of sample burning on the wire was conducted with a Vision Research

Phantom® v12.0 digital camera. The high speed video was taken at a resolution of 256×256 and frame rate of 67065 fps (14.9 µs per frame). The ignition temperature of the thermite sample reaction was obtained from the correlated high speed imaging of the ignition events with temperature profile of the Pt wire.

2.3.Pressure cell combustion tests: Simultaneous pressure and optical characterization

A constant volume combustion cell [13, 19] was used to characterize the reactivity of bulk thermite samples with the capability of simultaneous pressure and optical measurements. Typically, a fixed mass (25 mg) of the loose thermite sample was placed inside a constant-volume (~13 cm3) pressure vessel, and ignited by joule heating of a nichrome coil. A piezoelectric pressure transducer on the port of the cell, together with an in-line charge amplifier and signal conditioner were employed to measure the temporal pressure change and the pressurization rate (dP/dt). The pressurization rate has been used as a measure of reactivity in thermites since it has been found to correlate with flame propagation velocity, [20] another widely used measurement of thermite reactivity. The optical signal was simultaneously collected by a lens tube assembly attached on the port of the cell, containing a planoconvex lens (f = 50 mm) and a photodetector to collect the broadband emission. The characteristic burn time of thermites in the pressure cell was represented by the full width at half-maximum (FWHM) of the recorded optical signal. For the detailed combustion cell measurement, you can refer to our previous papers. [13, 19]

The mindicateof in ter 2.4.Post

The pcollecteadhered(TEM, interactienergy doperatedsample. 3. Resu 3.1. Timaluminu

Figure

I2O5 p

up to ~1resolvedsample t<1.0 m

measuremenes that both trms of relati

t-combustio

post-combud sample w

d onto a TEJEOL JEMion betweendispersive Xd in scannin

ults and Di

me resolved um

3. Time-res

particles as 1800 K, at d mass spec(microsize)

ms (also seen

nt of reactithe pressuriive performa

on character

stion produwas dry gro

EM grid (AuM 2100 FEGn the combuX-ray spectrng mode to p

iscussion

d mass spec

solved massbox an

well as thera heating ra

ctrometry. W) decomposin in t=0 s in

ivity of theization rate ance at the p

rization

ucts were coound by rubu mesh/carbG). This TEustion produrometer (EDperform 1D

trometry of

s spectra frond (b) milled

rmite samplate of 5×10We begin byition under

n Figure 5), p

5

thermitesand optical present time

ollected afteubbing betwbon film) foEM sample ucts (e.g. iodDS, Oxford ID elemental

f iodine pen

om I2O5 decd sample exp

es of nano-A5 K/s, and ty examiningrapid heatiprimary pea

is usually remission m

e.

er combustiween two veor analysis i

preparationdine) and soINCA 250)line scannin

ntoxide deco

omposition posed to air

Al/micro-I2

the species fg the time rng, shown aks of H2O

reported asmeasurement

ion test in tery clean gin transmissn techniqueolvent. The Tfor elementng and 2D e

omposition

(a) milled sr for one day

O5 were rapformed werresolved main Figure 3(m/z=18) an

a relative ts should on

the combusglass slides.sion electroe was used TEM is equtal analysis,elemental m

and reactio

sample prepy.

pidly heatedre examinedass spectra oa. For specnd N2 (m/z=

value, whinly be thoug

tion cell. T. The powd

on microscoto avoid an

uipped with which can

mapping of t

on with nan

pared in glov

d in ~3 ms and by the timof milled I2Octrum taken =28), togeth

ich ght

The der ope ny an be

the

no-

ve

nd me-

O5 at

her

with a sT=800 KIO2

+, I2+

iodic achygroscHI3O8 (awater (3signal, athe rapi4a. From~760 K.

Figurmilled s

In F

which wsample evolutioshown iFigure 3species tempera

Figu

I2O5 (mithe thersimultanwas fouobserve

small amounK (t=1.0 ms+, and I2O

+.cid (HIO3)

copic, this salso denote3I2O5+H2Oas well as I+

d heating om Figure 4a.

re 4. Temposample prep

Figure 3b, wwas exposedshown in Fi

on in the airin Figure 4b3b. Similar

which areature. The on

ure 5 shows icrosize) thermite reactineously cap

und to ignite O2

+, I+ an

nt of O2 (m/s), we found. It is noted decompos

suggests thaed as HIO3.I2HI3O8). +, I2

+are obsf milled I2O

a, the onset

oral profile opared in glov

we show thd to air for igure 3a . Cr exposed s

b contains mwith milled

e from the nset oxygen

the time reermite reaction, a high pture the eme at ~940 K d I2

+ prior

/z=32) are fd a strong s

d that I+, IOsition usingat the spectrI2O5) [22] wAt higher

served. We O5 sample a

temperature

of oxygen anve box and

e mass speone day an

Comparison sample is simore water, d I2O5 samp

decomposn release tem

solved mastion. In add

speed cammission fromK (t=1.70 ms

to ignition,

6

from the baignal assign

O+, IO2+ were

g mass sperum taken awhich formtemperaturealso plot Os a functione of oxygen

nd water pe(b) milled s

~5×105K

ctra taken and expectedof the two significantly it is not sur

ples shown ition of I2

mperature is

s spectra takition to the

mera systemm the ignitions) as optical, consistent

ackground spned to O2

+ ae previouslyectrometer.at ~800 K m

ms from reaces >910 K

O2+ and H2O

n of time ann release for

eak intensitysample expoK/s)

at rapid head to absorb samples (Fiabove the

rprising to sin Figure 3O5 (2I2O5

s ~740 K, as

ken at 100 μmass spectr

m was coupn and comblly observed

with the s

pecies in thand other sigy reported a[21] Given

might be froction betwe(t=1.3 ms),+ temporal

nd wire tempr milled I2O

y from heatiosed to air fo

ating of anomuch more

igures 4a-b)background

see a higher3a, only stro5O2+2I2) s shown in F

μs intervals rometry me

pled with thbustion procd by the higtraight deco

he ionizationgnals assignas the priman the fact om the decoeen iodine p, only a verintensity obperature sho

O5 particles i

ing of I2O5 sor one day.

other millede water tha) clearly shod. Since ther intensity oong O2

+ signcan be se

Figure 4b.

for a nano-easurement he mass spcess. The theh speed camomposition

n chamber. ned to I+, IOary species

that I2O5

omposition pentoxide ary strong O

btained duriown in Figuis found to

samples. (a)(Heating ra

d I2O5 sampan milled I2Oows that wate I2O5 sampof IO+, IO2

+

nal and I+, Ieen at high

Al and millconducted fectrometer ermite sampmera. We al

of I2O5. Po

At O+,

of is of nd

O2+

ng ure be

) ate

ple O5 ter ple in

I2+

her

led for to

ple lso ost

ignitionpeak waobservethe amodecompoxidizer

Secon

from I2O

3.2.Com

The i

conditioAl/I2O5 ignitionignitionmechanpreviou

n, we find stas also obsd are consis

ount of oxyposition, impr.

ndarily, we O5 (~740 K)

Figure 5.

mbustion cha

ignition behons by high-

thermite ren at t=1.491 n points thanism, consistsly suggeste

trong signalserved afterstent with th

ygenated iodplying not

also see th) and essent

A

Time-resolv

aracterizati

havior of na-speed imageactions at ms, correspat propagattent with hoed to explain

s for O2+ an

r ignition, phe global re

dine speciessurprisingly

at ignition (tially at the p

2I2O52IAl+I2O5A

ved mass sp

on of nano-

ano-Al/micrging. In Fig

atmospheriponding to tte toward eot O2 convecn high prop

7

nd I+ and wepresumably eaction press is reducedy that the io

(~940 K) ocpoint that al

I2+5O2

Al2O3+I2

pectra from

-Al/micro-I2

ro-I2O5 thergure 6, we sic pressure.the wire temeach other ctive heat tr

pagation rate

eaker signalfrom some

sented in Eqd in the therodine sub-o

ccurs after tluminum m

Eq. (1) Eq. (2)

nano-Al+m

O5 thermite

rmites sampshow selecte. The imag

mperature ofand are s

ransfer effeces for Al/Ag

ls from I2+ a

e water in q. 1 and 2. rmite as co

oxides can a

the point ofelts (933 K)

micro I2O5 th

es

ples were eed temporal

ges allow uf ~810 K. Thsuggestive cts. In fact, tgIO3 burning

and I2+. A vthe sampleOne point ompared witalso act as

f gas phase ).

hermite reac

examined inl snapshots

us to assignhe images aof a flamethis explanag on the wir

very weak IO. The speciof note is thth the straigan aluminu

release of O

ction.

n atmospherof the viole

n the point also show twe propagatiation has bere. [1] Herei

O+ ies hat ght um

O2

ric ent of

wo on

een in,

we notebe 100 dexplainedecomp

Figure speed

In the

displayethat a hicomparestill highreactivitmean frand so sbefore it

Constnano-Alnoted theffects oI2O5 andas receiv

DirecFigure 7and a shhigher p[6]

The e

thermite

ed that the idegrees lowed by the

position and

6. Sequentid video cam

nano-Al

e ionizationed a much leigher ignitioed to~810 Kher than thety and burnee path of gsome oxyget reacts with

tant volumel/micro-I2O5

hat all thermof particle sd nano-Al/mved I2O5 the

ct compariso7c-d. The phorter burnipeak pressur

experimentaes along w

gnition temwer than the

possible ethe aluminu

ial snapshotmera. The lab

l (ALEX) an

n chamber oess violent ron temperatuK in air at ate oxygen reling in vacuu

gas released en released h the alumin

e combustio5 thermites

mite formulasize we plot micro-I2O5 iermite in ter

on of the coplots show thing time. Thre than Al/C

al results ofwith other m

mperature formelting poi

exothermic um oxide sh

ts of Al/I2O5

beled numbnd milled I2

of mass spereaction andure was foutmosphericlease tempeum and air from the oxfrom the I2

num nanopa

on cell testsagainst oth

ations in thisimultaneo

in Figure 7arms of a hig

ombustion chat I2O5 hahe same trenCuO combu

f pressure ametal oxide

8

r Al/I2O5 syint of the alu

reaction bhell surroun

5 burning oners are time

2O5 (microsi

ectrometer (d burning thund for the n

pressure. Herature fromcan be furthxidizers in vO5 particles

articles.

s were perfher thermiteis investigatous pressurea-b. Quite cgher pressure

cell tests ofs a higher ond is also re

ustion in whi

and optical s thermite

ystem in airuminum. Thbetween proding the Al

n fast-heatine elapsed (μsize) with an

(~10-6 Torrhan at atmosnano-Al/mic

However, ignm the I2O5 paher explainevacuum is ors may simp

formed to ees under attion use the e and opticalclearly the me peak, shor

f Al/I2O5 anoverpressureeported elseich both fue

emission damixtures in

r at atmosphhe low ignitoducing ionanoparticl

ng wire in ais) after trigg

n equivalenc

r), the nanospheric condcro-I2O5 thenition tempearticles (~76ed from the rders of maly escape fr

evaluate thetmospheric same nano

l traces for bmicro-I2O5 rter pressure

nd nano-Al/me by a factoewhere that el and oxidi

ata are furthn Table 1.

heric pressution temperadine from les. [4]

ir, as capturgering. The ce ratio of 1

-Al/micro-Iditions. It isermite in vaceratures in b60 K). The following agnitude highrom the the

e relative peconditions. -Al fuel. Toboth nano-Athermite oue rise and bu

micro-CuO or of ~ 4 reAl/I2O5 dis

izers are at t

her tabulateClearly, th

ure is found ature might

the oxidiz

red by a highthermite is .0.

I2O5 thermits worth noticuum (940 Kboth cases adifferences approach. Ther than in armite mixtu

erformance It should o compare tAl/as receivutperforms turning time

are shown lative to Cusplays a muthe nanosca

ed for Al/I2Ohe micro-I2O

to be

zer

h-

tes ng K), are of

The air, ure

of be

the ved the .

in uO uch ale.

O5 O5

thermiteall other

Figurethermit

nan

In a p

peaks eoptical spressurepressuribefore ssame stuwe concall nanooptical sAl/CuOsystem CuO sydecomp

e exhibits thr nano-Al/m

e 7. (a) presstes reaction

no-Al+micro

previous stuarlier than signal. [17]e rise time ization occusignificant cudy with Acluded that o-Al/micro-osignals occu

O nanothermis quite diff

ystem is the position has

he highest omicro-oxidiz

sure and (b)ns; (c) pressuo-CuO therm

udy of nanodoes the op The result (13 μs) a

urs as a resucombustion

Al/Fe2O3 forthe oxidizeoxidizer theur almost co

mite system, fferent. Give

particle sizs become t

overpressurezer thermite

) optical tracure traces anmites reactio

constant

othermites, ptical emisscan also be

and a relatilt of the oxy

n as associar which the er decomposermites formoncurrently,indicating t

en the only ze of the Cuthe rate-lim

9

e and pressusamples an

ces for nanond (d) opticaons. All of tt-volume co

we found tsion. i.e. a e seen in Taive long buygen releaseated with th

pressure ansition was th

mulations tab or even earthat the reacdifference

uO oxidizermiting step

urization ratd even a nan

o-Al+as receal emission the results mombustion ce

that for therapid pressu

able 1 for nurn time (1e from CuO

he optical emnd optical she rate-limibulated in Trlier. This isction mechafor Al/CuO

r, it is reasoin nano-Al

te, and shorno-Al/nano

eived I2O5 atraces for n

measured duell.

e Al/CuO nure signal fano-CuO, w

192 μs). W nanoparticlmission. Thignals occuiting step inTable 1, we s very differanism in the

O nanothermonable to col/micro-CuO

rtest burning-Fe2O3 therm

and nano-Alnano-Al+miluring combu

anothermitefollowed bywhich show

We have argles, which c

his was conur concurrenn Al/Fe2O3.

can see therent than thae nano-Al/m

mites and naonclude thaO thermite

g time amomite.

l+milled I2Olled I2O5 an

ustion in a

e the pressuy a prolongs a very shogued that tcan occur wntrasted in tntly for whiHowever, f

e pressure anat observed

micro-oxidizano-Al/micrat the oxidiz

reaction. B

ng

O5 nd

ure ged ort the ell the ich for nd in

zer ro-zer By

10

extension then this argument implies that oxidizer decomposition is limiting in the nano-Al/micro-I2O5 thermite reaction for which pressure and optical signals occur concurrently.

Table 1. Combustion cell test data for thermites samples prepared with different oxidizers. All oxidizers were mixed with nano-Al (ALEX). Thermites samples were prepared stoichiometrically

assuming complete conversion to Al2O3.

Oxidizers (w/Al, φ=1)

Prise

(KPa)

Pressure rise time

(μs)

Pressurization Rate

(KPa/μs)

FWHM burn

time (μs)

Note

I2O

5 (A) 237 944 0.251 1579 As received, Sigma-Aldrich, 99.99 %

I2O

5 (M) 366 397 0.922 293 After 1 hour milling

Micro-CuO 152 732 0.208 514 <5 μm, 98% ,Sigma-Aldrich Micro-Fe

2O

3 51.7 8350 0.00619 4394 <5 μm, ≥99%, Sigma-Aldrich

Nano-CuO 800 13 61.5 192 <50 nm, Sigma-Aldrich

Nano-Fe2O

3 92.4 800 0.116 936 <50 nm, Sigma-Aldrich

Thermodynamic equilibrium data for Al, Fe2O3, CuO and I2O5 based thermites taken from Fischer

and Grubelich’s theoretical calculations [23] are shown in Table 2. From the data both the Cu and I based systems should be significant gas producers relative to Fe, and is in fact consistent with the pressurization data presented in Table 1. The experiments however show that I2O5 generates a pressure rise more than four times that of of nano-Al/micro-CuO system, indicating the faster reaction kinetics. The higher maximum pressure can be explained by the fact that the evaporation of low boiling point iodine (457 K) could increase the pressure inside the reactor while the boiling point of metal product formed during Al/CuO thermite reactions is much higher than iodine. [6] Table 2 Constant enthalpy and pressure thermodynamic equilibrium calculations of stoichiometric

thermite systems. Data is taken from Fisher and Grubelich (1998) without taking account of the oxide shell on Al.

Thermite reaction Adiabatic

Temp. (K)

Gas production(mmol/g)

Major gas species

State of metal

2Al+Fe2O

3-> Al

2O

3+ 2Fe 3135 1.4 Fe liquid-gas

2Al+3CuO-> Al2O

3+ 3Cu 2843 5.4 Cu liquid-gas

10Al+3I2O

5->5Al

2O

3+3I

2 >3253 6.3 I

2 gas

For all thermites reactions limited by the decomposition of oxidizers, the pressure rise is largely

dependent on the final state of the products other than the gas produced during the decomposition of oxidizers. Next, it will be very straightforward for us to understand why the nano-Al/micro-CuO and nano-Al/micro-I2O5 can even outperform the nano-Al/nano-Fe2O3 thermite reactions in terms of relative combustion performance shown in Table 1.

In addition, from the point of view of Al/I2O5 thermite’s potential application as biocides, it has

been expected that the pressure rise is from the produced hot biocidal species by very exothermic

thermiteAl/micrvery gobehave nanosizesignal. Overy dif 3.3. Pos

Not oproductnanoparproducin

The pethanol,The samTEM anelementAl/I2O5 particlesproductsmall nathe posseffectiveiodine environm

Figure combus

Al (A

e reactions ro-I2O5 thermood candidasimilarly ined oxidizersOf course, wfferently, an

st-combustio

only the cos matter inrticles have ng biocidal

post combus, the resultemple was alnalysis. A tal map of Athermite. F

s only conts are aluminanoparticlessibility of the way to prcondenses ment thus m

8. Represenstion producALEX) and

element

other thanmites formuate for effen the combs. That is towe cannot r

nd more exp

on characte

ombustion pn biocidal a

higher cell products wh

stion produced solution lso dry grourepresentatiAl, O and IFrom the eltain I. Selecnum oxide as (with darkhe AlI3 formroduce iodito form th

maximize its

ntative TEMcts after Al+milled I2O5

t has a dark

n species fulations witective biocbustion cell say, the higrule out the erimental st

erization of A

performanceapplications

cytotoxicityhich have a

cts of Al/I2Odisplayed a

und by rubbive transmiI is shown emental macted particleand iodine, ak contrast) cmation in thne gas via he high sus killing pot

M image and+I2O5 therm5 particles (mcontrast in

11

from the deth concurrenides. Sincetests, we w

gher pressurpossibility

tudies are ne

Al+I2O5 the

e of thermi. Numerousy. [24, 25] high surfac

O5 thermitesa brown colbing betweeission electrin Figure 8

apping, we es with an as shown inconfirmed bhe final prod

condensed urface area tential as a b

d 2D elemenmite reaction

microsize) wTEM image

ecompositiont pressure

e nano-Al/mwould expere rise occurthat two oxeeded to ver

ermites

ites, but alss toxicologiSo, a good

ce area and c

s reaction wlor indicatinen two veryron microsc

8 for producsee particleelemental l

n Figure 9. Ty EDS in F

ducts. In simphase reactnanopartic

biocidal age

ntal mappingin the comb

with an equie because of

on of oxidiand optica

micro-CuOect similar crs much earxidizers at nrify this.

so the naturical studiesbiocide syscan be expo

were collecteng the iodin

y clean glasscopy (TEMcts from thees that continescan cou

The produceFigure 8-9. Tmple, Al/I2Otion. Furtheles with sunt.

gs (Al, O, anbustion cellivalence ratif its high ato

izers. Hencal rise signa

and nano-Acombustionrlier than opnanoscale m

re and disps have showstem shouldosed to the e

ed and addene formed as slides and

M) image ale combustiotain Al and upled also ced iodine speThe results O5 thermite ermore, upourface expl

nd I, using E. The thermio of 1.0. Noomic numbe

ce, the nanal should beAl/micro-I2O

n behavior ftical emissi

might behavi

persion of twn that smd be a reactienvironment

ed up with tafter reactiod prepared flong with ton cell test

O, and othconfirmed tecies exists also excludreaction is

on cooling tlosion to t

EDS) of pos

mite was nanoote: Iodine er.

no-e a O5 for on ior

the all on t.

the on. for the of

her the as

ded an

the the

st-o-

Figure

4. Con

The i

Mechansystem mass spand iodreactionthat nanand buroxidizerthis studCuO syspecies oxidizerand theConsideeffectiveiodine environm Acknow

This rWe acknsupporte

e 9 TEM imareaction in

nclusions

gnition andnical millingwas found

pectrometry dine speciesn in air at ano-Al/microrning time. r systems indy is possibstem, the prby very e

rs. TEM coue results inering its poe way to prcondensed ment thus c

wledgement

research wanowledge thed in part by

age and 1D n the pressu

d combustiong was succeto have a hshows that

s, mainly I+

atmospheric o-I2O5 system

Concurrenn this study.bly limited ressure rise exothermic upled with E

ndicated thaotential approduce iodito form thould maxim

ts

as funded byhe support oy the NSF a

elemental lure cell. Not

n behavior ossfully applhigher reactI2O5 oxidiz

+ and I2+. T

pressure wm outperfor

nt pressure . This suggeby the decoin nano-Al/thermite re

EDS analysat the prodplication ane gas via he high su

mize its killin

y the Defensof the Marylas a MRSEC

12

linescan (usite: Iodine na

of nano-Al/mlied to prepativity compazer starts toThe ignition

was determinrms nano-Aand optica

ests that theomposition /micro-I2O5

eactions otsis was perfoduced iodins biocides,condensed

urface area ng potential

se Threat Reland Nanoce

C Shared Ex

ing EDS) acanoparticles

micro-I2O5

are microsizared beforedecompose n temperatuned to be ~

Al/micro-CuOal rising wae burning ofof oxidizer

5 in this studther than spormed to ane species c nano-Al/mphase reactnanopartic

l as a biocid

eduction Agenter and its

xperimental

cross particls formed and

thermite waze I2O5, and mechanicaat 760 K to

ure of nano~810 K. ComO system inas observedf nano-Al/mrs. Differentdy is from tpecies from

nalyze the pcondensing micro-I2O5

tion. Furthecles with sudal agent.

gency and ths NispLab. TFacility.

les formed ad no AlI3 fo

as systematid the milled al milling. To produce a o-Al/micro-mbustion cen both pressd for all namicro-oxidizt than the nthe producedm the decoost combusas small n

thermite reermore, upourface expl

he Army ReThe NispLa

after Al+I2Ound.

ically studieI2O5 therm

Time resolvlot of oxygI2O5 thermell tests shosurization raano-Al/micrzer systems nano-Al/nand hot biocid

ompositiontion producnanoparticleeaction is on cooling tlosion to t

esearch Offiab is

O5

ed. mite ved gen

mite ow ate ro-in

no-dal of

cts, es. an

the the

ice.

13

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