Activated Aluminum Powders for Space Propulsion

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This is the accepted version of:

F. Maggi, S. Dossi, C. Paravan, L.T. De Luca, M. Liljedahl

Activated Aluminum Powders for Space Propulsion

Powder Technology, Vol. 270, 2015, p. 46-52

doi:10.1016/j.powtec.2014.09.048

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https://doi.org/10.1016/j.powtec.2014.09.048

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© 2015. This manuscript version is made available under the CC-BY-NC-ND 4.0 license

FilippoMaggi a,1,

∗

Polite ni o diMilano, 34,viaLaMasa,20156 Milan, Italy b

SwedishDefen eResear h Agen y,FOI, SE-14725Tumba,Sweden

Abstra t

Aluminum powders are ommonly used in solid propellants to enhan e the

performan e of spa e propulsion systems. During ombustion, a fra tion of

the fuel metal parti les, whi h emerge from the bulk, tends to merge into

aggregates. These stru tures eventually leave the ombustion surfa e in the

shapeofpartiallymoltenagglomerateswhi h anrea hthesizeofhundredsof

mi rons. These ondensed ombustionprodu ts partakeinnozzleexpansion

andhinderthedeliveredspe i impulseofthero ketunit. Theenhan ement

of original parti le rea tivity improves ombustion quality and may redu e

sensibly agglomerate size and relevant losses.

More rea tive aluminum fuel an be obtained by a tivation of

mi ron-sized powders, without resorting to the use of nano-metals. One of the

methods onsists of a hemi al treatment with a pro essing solution whi h

alters the standard oxide layer at the surfa e of the parti les. Su h

modi- ations grant lowerignition temperatureand faster propellantburningrates

∗

Correspondingauthor,Tel. +390223998287

Email addresses: filippo.maggipolimi.it(FilippoMaggi),

stefano.dossimail.polimi.it(StefanoDossi), hristian.paravanpolimi.it

(ChristianParavan),luigi.delu apolimi.it(Luigi T.DeLu a),

mattias.liljedahlfoi.se(MattiasLiljedahl) 1

Department of Aerospa e S ien e and Te hnology, Spa e Propulsion Laboratory

(SPLab) 2

rea tion.

The present paper ompares the features of three bat hes of aluminum

parti les whi h were treated with uorine-based a tivating solutions of

dif-ferent on entration. The bat hes were supplied in the frame of HISP FP7

European Proje t. The hara terization fo used on physi al, hemi al and

thermalproperties,lookingattherea tivity ofthe samplesand atthe

alter-ations introdu ed by the hemi al pro essing. Finally, a tivated aluminum

bat hes were tested inlab-s alepropellants,monitoring the variationof

bal-listi properties with respe t toa referen e formulation.

Keywords: aluminum parti les, hemi ala tivation, rea tivity, solid

propellant,metal fuel

Nomen lature

A ronyms

BET Brunauer-Emmett-Teller

DTA Dierentialthermal analysis

ESD Ele tro Stati Dis harge

FCC fa e- entered ubi

SEM S anning ele tron mi ros opy

TGA Thermalgravimetri analysis

TMD Theoreti al mean density

XPS X-ray photoele tron

spe -tros opy XRD X-ray dira tion Greek symbols

α

∆x

ρ

g/cm

3

C

A tive metal fra tion

D

4,3

m

Subs ripts and supers ripts

in Initial ondition

zK Ref. to the temperature of z

Kelvin

1. Introdu tion

Gravimetri and volumetri spe i impulseofsolidro ketmotors anbe

enhan ed by using energeti additives [13℄. Among the others, Aluminum

hasbeenadopted insolidspa epropulsionforde ades,intheshapeof

mi ro-metri metal powders, thanks to its appealing energeti ontent (30 kJ/g),

stability intime, non-toxi ity, and relatively low ost. Typi alparti le sizes

range from 5to 50mi rons[4, 5℄.

Afra tion of themetal embeddedin apropellant tendstoaggregate and

agglomerate during ombustion. Drops of molten aluminum with an oxide

ap leave the burning surfa e [6, 7℄. These ondensed ombustion produ ts

generate a multiphase ow whi h expands through the nozzle. Performan e

losses are the order of 2-5% of the ideal spe i impulse, depending on size

and amount of the parti ulate [8, 9℄. In this respe t, the improvement of

metal fuel ignition and ombustion is envisaged in order to obtain ner

ag-glomerates, or noagglomerationatall [3,10℄.

Aluminumparti lesare overed by anaturaloxide layer, assoonasthey

get in onta t with oxygen- ontaining environments. This passivation shell

represents a strong shield against further degradation by the atmospheri

oxygen. At the same time, it represents an obsta le to rea tivity. Under

burning onditions, ignitiono urswhen the passivating aluminashell fails,

enabling fast oxidation of the metal ore. The melting temperature of the

par-as 1300 Kwere re orded in presen e of some kindsof a tive media (namely,

ombustionprodu tsinsidero ket oreow)[11℄. Ignitiontemperatureis

be-low900-1000K,fornanometri powders. Parti lestakeadvantage ofsample

spe i surfa e and a tive oating layers, if any [12℄.

Literature data agree on the fa t that the use of nanometri parti les

inpropellantsimprovesignitionand ombustionproperties, preventing from

largeagglomerates[1315℄. However,theredu tionofparti lesizeintrodu es

somedrawba ks. Therelativeamountofaluminumoxidewithrespe ttothe

total parti le mass an be ome relevant in the nanometri range, sin e the

thi kness of the oxide layer (about 2.5-3 nm) does not s ale with parti le

size [16℄. The onsequentredu tionof thea tivemetal ontentdepresses the

available oxidation enthalpy and, in turn, propulsion performan e (namely,

ideal spe i impulse). Moreover, mixing and asting of a propellant

on-taining nanometri ingredients may represent a te hnologi al issue due to

high vis osity, redu ed pot life, ESD (Ele tro Stati Dis harge) and impa t

hazards aswell as ost of the manufa tured ompound [17℄.

Spe i a tivation pro esses an be performed on metal parti les to

im-prove ignition and ombustion properties, without de reasing the diameter

tothesub-mi rometri range. Me hani alballmilling, oatingwithproperly

hosen metals, or hemi al weakening of the external oxide layer represent

some examples. Me hani al milling operates amodi ationof parti le

mor-phology by high-energy impa t with pro essing spheres. Synthesis of

amor-phouspowders,stru ture hange,produ tionofmetal- erami s,orin lusions

of rea tants (metal oxides or uorides) an be a hieved [1821℄. Coating of

parti les through deposition of metals an improve ignitionand ombustion

ride a ts assolventfor alumina,lowering the meltingpointof the prote tive

aluminumoxidelayeraswellasa eleratingthediusionof gaseousoxidizer

towards the metal ore [25, 26℄.

Thepresentpaperfo usesontheee tsprodu edbya hemi ala tivation

pro ess. Aluminum powder treated with three dierent a tivating solutions

of varying on entrations are onsidered. Physi al, hemi al, and thermal

hara terizations, typi ally applied to nanometri powders, are performed

to evaluate rea tivity and nal quality of the material[13, 27℄. Comparison

withoriginalnon-treatedmi ron-sizedAlaswellaswithsomerepresentative

literature data for nanoaluminum and mi roaluminum is arried out.

Com-bustionanalysisofsolidpropellantsamples ontaininga tivatedpowdersare

presented.

2. Experimental

Three bat hes of a tivated aluminum powders (A-Al01, A-Al02 and

A-Al03)havebeenprodu ed, followingapro eduresimilartotheonedes ribed

by Hahma[25,28℄. Theinitialaluminumwas ValimetH3powder(bat h

07-8002). The produ er rated 99.0% of minimum metal ontent and parti le

size of 4.5

µ

uorine-basedsolution,whose on entrationwasvariedtomodifythestrength ofthe

treatment. The bat h A-Al01 was assumed as referen e for the pro essed

family. The on entration of the solution was the half for A-Al02 and 1.5

timesforA-Al03. Powderpro essingwas ondu tedatFOI(SwedishDefen e

Resear h Agen y), aspartof the HISP(HighPerforman e SolidPropellants

for In-Spa e Propulsion) FP7 proje t.

s ans. Dierent omposite solid ro ket propellants were ompounded and

their ballisti properties were experimentallytested. Moreover, the

ontra -tion of ideal performan e, followingthe depletion of metalli aluminum

dur-ing a tivation, was monitored by means of thermo hemi al analysis [30℄.

2.1. Physi al hara terization

SEM mi rographs, reported in Figure 1, show a omparison between

Valimet H3 and all a tivated bat hes. Parti les appear mainly spheri al.

The external surfa e is smooth for the original powders and rough for the

pro essed ones. The a tivated parti lesalsofeature some irregulardeposits,

notpresentintheoriginalmaterial,whosesizeseemstofollowthe

on entra-tionofthea tivatingsolution. Namely,thespots overingtheA-Al03surfa e

rea h the size of about 100 nm, whereas smallerdimensions are observed in

the other ases. A pre ise estimation is di ulttosupply.

[Figure1 about here.℄

Parti lesizewasmeasuredbymeansofaMalvernMastersizer 2000using

airdispersion withS iro o dryunit. Mass-meandiameter

D

4,3

distribution, and evaluation for the spe i surfa e, derived from geometri

onsiderations, are reported in Table 1. Valimet H3 and a tivated powders

do not demonstrateappre iable dieren es. All parti leshave a omparable

mass-weighted diameterranging between 5.1 and 5.5

µ

distri-bution shape and relevant span. For all a tivated powders, mean parti le

diameter grows few hundreds of nanometers. Representative distribution

Table1: Parametersforphysi al parti le hara terization. LiteraturedataofALEX and ASD-4are reportedforreferen e. Spe i

surfa eareasderivefrombothBETmethodandparti lesize analysis.

Id. H3 (baseline) A-Al01 A-Al02 A-Al03 ALEX

TM a

ASD-4 b

A tivatingsolution relative on entration 0 1.0 0.5 1.5 -

-D4,3, µm

Span 1.78 1.66 1.68 1.64 -

-Spe i surfa e area,

m

2

_/g

(BET) 1.2 2.6 2.2 3.3 11.8 0.38

Spe i surfa e area,

m

2

_/g

ner than 1

µ

observed.

[Figure2 about here.℄

A more representative evaluation of the powder spe i surfa e is

a - omplished using the BET te hnique [33℄. The estimation is based on the

quantityofadsorbed inertgasonthesurfa eofasample. Theresultdepends

onboth geometri aspe t of the parti lesand onthe pe uliaritiesof the

sur-fa e (namely,roughness) [35℄. A ording toBarret, parti le hara terization

isa omplishedwhensize,shapeandnishareaddressed[36℄. Bouwmanand

o-authorsstressonthefa tthatsurfa eroughnessandshapearedi ultto

denesin etheir distin tionderives,ingeneral,from onsiderationson

har-a teristi dimensions whi h, in turn, depend on the observation s ale [37℄.

In this respe t, the spe i surfa e measurement using the BET te hnique

is a ondensed and omprehensive value, whi h in ludes all ontributions.

This kind of analysis has been adopted in the past to hara terize ne and

ultra-ne metal powders, alsoforenergeti purposes. The measurementwas

onsidered a reliableindex of rea tivity [10, 34℄.

The resultingtrendamongthe testedbat hes is orrelated with the

on- entration of the a tivating solution. The spe i surfa e from BET

analy-sis is in remented by the a tivation pro ess. The referen e A-Al01 doubles

the spe i surfa e, if ompared to the original H3 supply. A-Al02 features

the lowest BET improvement while A-Al03 has the highest value,

respe -tively less-than-double and almost three times the value of H3 bat h. Laser

granulometry assessed that the mean diameter of the parti les was almost

un hanged by the hemi al pro essing so the variation of spe i surfa e is

attributed to porosity in rement. These results are in agreement with SEM

The quanti ation of the metalli aluminum in the powder, after the

hemi al pro essing,is performed by hydrolysis. The moles ofH

2

by samples,on e in onta t with water, are monitored in time till

stabiliza-tion is obtained. A solution of NaOH (10% on entration by mass) is used

to dissolve the external oxide shell and fa ilitate the pro ess. Following a

standard volumetri method[38℄, the assumed stoi hiometri rea tionis

Al + 3 H

2

O → Al(OH)

3

+ (3/2)H

2

↑

+

The moles of rea ted metal fromthe evolved hydrogen an be determined.

This hemi ala tivationpro ess hastheunwel omeee t todepletepart

of the aluminum from the powder. The metal ontent of the initialpowder

bat h was quantied in more than 98%. Tests on a tivated samplesshowed

a onsistent ontra tion of the Al ontent. The de rement was only in part

dependent on the on entration of the a tivating solution. For the powder

whi hunderwentthestrongesta tivation(A-Al03),only90%ofparti lemass

was estimated tobea tivealuminum. For A-Al01 and A-Al02, the fra tion

was around 93%.

X-ray analyses were alsoperformed onthe samples. Forall the powders,

XRD identiedthe presen eof aluminum only,infa e- entered ubi (FCC)

rystalline form,regardless of the a tivation. The dira tionpatternfor the

A-Al01sampleis reported inFigure3. The resultindi atesthatthe

super- ial hemi al treatment did not generate dete table quantities of rystalline

ompounds. The sampleswere furtheranalyzed withXPS, foridenti ation

of surfa e elemental omposition. Dierent atomi spe ies were introdu ed

by the a tivation pro ess, su h as uorine, present with a 13.0% atomi

17.0% and oxygen 58.0%.

[Figure3 about here.℄

2.3. Thermogravimetri analysis

The ee ts of enhan ed parti le rea tivity on intensive oxidation onset

and other related parameters were analyzed by means of TGA/DTA in air

atambientpressure. S answereperformedon10mgsampleswith10K/min

heatingrate,up to1273K(1000

◦

C).As representatives, the s ansof A-Al01

and of H3 baseline are reported in Figure 4, using the same s ales on the

axesfor immediate omparison. Overallresultsare reportedinTable 2. The

DTA tra e of A-Al01 shows an oxidation peak, overlapped to the melting

of the aluminum ore, in proximity of 933 K. The rea tion is forerun by an

initial exothermi release. From the analysis of peak positions for dierent

a tivated materials, it appears that stronger a tivation does not anti ipate

the oxidation onset towards lower temperatures. The baseline H3 powder

did notshowproofsoffastoxidationinthe samerangeoftemperature. This

behavior is in line with past experimental ndings, available in the open

literature. The ignition of standard mi rometri powders is size-dependent

and, for therange of interest,fast oxidationis expe tedto o ur above1273

K (1000

◦

C). [39℄.

The degree of transformation

α

value of

α

ini-tialsamplemass

m

whi hturnedintoitsoxide. Themeasureisbasedonthe

re orded massin rement

∆m

and onthe initiala tivemetalfra tion

C

of therespe tivebat h,quantiedwiththe volumetri methoddes ribed

onversion of Al into

Al

2

O

3

α (Al → Al

2

O

3

) =

∆m

0.889

1

m

C

In onsiderationof TGAresults,the degreeof transformationwas evaluated

at three referen e temperatures and, namely,

α

933K

melting,

α

973K

α

1273K

nals anningtemperature1273K.A orrelationbetweena tivationstrength

and degreeof metaloxidation was missingeven though a generalin rement

of the oxidized fra tion was observed at the end of the test for a tivated

powders.

When DTA/TGA tra es for A-Al01 and H3 are ompared (see Figure

4), a dierent rate of weight in rement and, as onsequen e, of oxidation

an be observed. The H3 sample progressively in reased its mass during

the whole TGA s an. Rather, A-Al01 showed an abrupt in rement during

the exothermi peak, indi atinga fast oxidation rea tion. However, most of

the metal-oxide onversion o urred while thealuminum ore wasalready in

liquidstate, meaningthat metal onsumptionatparti leignitionwasrather

limited.

[Figure4 about here.℄

2.4. Appli ation in propellants

The inuen e of powder a tivation on solid propellant properties was

assessed. Four aluminized formulations based on AP oxidizer and HTPB

binderwere produ ed, using dierent bat hes of metalfuel. The same

Table2: Parameters for hemi alandthermalparti le hara terization. ALEX andASD-4properties,available fromtheliterature,

arereportedfor omparison.

Id. H3 (baseline) A-Al01 A-Al02 A-Al03 ALEX

TM a

ASD-4 b

A tivemetal, % 98.3

±

±

±

±

DTA oxidationpeak,K N.A.

934 K 943 K 939 K 876 1093 (onset)

∆m

-α

933K

α973K

-α

1273K

derswhilethebaselineformulation ontainedtherawH3non-a tivatedmetal

fuel. The hara terizationa tivity onsistedofthemeasurementofbulk

den-sity, porosity,and relevant ballisti data redu tion.

[Table 1 about here.℄

Propellantdensity

ρ

p

dif-feren e

∆ρ

p

evaluated using the formula

∆ρ

p

= (ρ

p

−

ρ

id

) /ρ

T M D

ombus-tion tests were arried out in a losed ombustion hamber, equipped with

automati pressure ontrol system, in a range between 5 to 40 bar.

Burn-ingratewasassessed throughopti alte hniqueusing theSPLab proprietary

software Hydra. The ensembleof resultsisreportedinTable 4while graphi

omparison of burningrate urves is available in Figure5.

[Figure5 about here.℄

[Table 2 about here.℄

Theuse ofa tivated metalfuelsimproved ballisti propertieswithout

in-trodu ing pe uliar issues for propellant ompoundingand uring. Low level

porosity wasdete ted. The presen e of the a tivation layer did not intera t

with uring pro esses or generated internal bubbling, at the mixing

tem-perature of 36

◦

C. These observations are in line with binder-fuel vis osity

analyses re entlypublished bythe sameresear hgroup[41℄. For ombustion

tests,anin reaseofburningrateintheorderofabout

+20%

the original non-a tivated powders, was observed. The in rement was

irre-spe tive of the typeof a tivation. Onlyminor dieren es were found among

data andrelevantttingsare reportedinFigure5. The urvesforP-A-Al01,

P-A-Al02, and P-A-Al03 are overlapped, suggesting that the dierent

on- entrationlevelsofthe a tivating solution,tested inthis framework,did not

modify the ombustion behaviorof the propellants.

3. Dis ussion

Theimprovementof parti lerea tivityafterthe hemi ala tivation

pro- ess is registered by both the in rement of the spe i surfa e area (visible

from BET analysis) and by the redu tion of parti le ignition temperature

below1273 K(observed inTGA/DTA tra es). The improvementof the

for-mer rea tivityparameteris ausedby thegenerationofsuper ialroughness

and is partially responsible of earlier parti le ignition. However, the latter

benets also from oxide layer weakening. It is not possible to weight the

dierent ontributions, so far. In this respe t, BET analysis re ords

par-tiallythe signi ant role of the a tivating solutionand the knowledge of the

ignition temperature supplements the hara terization.

Thea tivationpro ess ausedonlyasurfa e modi ation ofthe raw

ma-terial. XRD dira tionpatterns did not reveal any in-depth modi ation of

the rystalline stru ture, being the ore stillaluminum. XPS dataidentied

several atomi spe ies, laid by the hemi al pro essing on a thin super ial

layer.

It was veried that the amount of the a tive metal ontent was redu ed

even down to 90%. This latter aspe t be omes ru ial from a propulsion

pointof view. The enhan ement of powder rea tivity is performed with the

purpose to redu e metal agglomeration during ombustion and alleviate a

mounts the potentialgain for a better ombustion and more e ient nozzle

expansion. A quanti ationof su h ee t is reported inFigure6. The ideal

spe i impulse for the referen e propellant formulation, reported in Table

3,is omputedthroughthermo hemistry[40℄. Expe ted ontra tionisabout

1-2%, depending on a tivation strength and depleted metal. The redu tion

of two-phase owlosses annotbeassessed in this ontext ,nevertheless the

performan e detriment is quantied in the open literature as 3-5%. That

is, the improvement delivered by hemi al a tivation of aluminum may be

omparabletothenegativeee t ausedby the ontra tionofthe aluminum

ontent. Carefulevaluationof formulationingredients isenvisaged.

[Figure6 about here.℄

TheTGA/DTA s ans withlowheatingrate inoxidizing atmosphere(air

inthe present ase)indi atethe improvementofrea tivityfor a tivated

alu-minum parti lesathigh temperature. Exothermi peaksare obtained about

themeltingpointofaluminum. Atthesametimesampleweightin rementis

promptly re orded. Su h events are not visible for unpro essed H3 powder,

in agreement with the literature. Available data suggestthat fast oxidation

rateshouldbea hieved beyond1273K(experimentallimitofthispaper),for

unpro essed powders having similar size and shape. In general, aluminum

parti leignition,under ombustion onditions, istriggered bythe disruption

of the oxide layer. This event o urs after the melting of the oxide shell

(around 2300 K) for the mi rometri range, or is aused by the expansion

of the parti le bulk for the nanometri size [39℄. In this ase, the

exother-mi peak and the onsequent fast oxidation rate from DTA/TGA s ans are

overlapped with the melting of the aluminum. It is possible that the oxide

the powder whi hdid not grant enoughspe i surfa e area.

A tivated aluminum powders result in intermediate properties, globally

ranking their rea tivity above omparable mi ron-sized aluminum, though

still far from nano-sized parti les. Tables 1 and 2 report some relevant

lit-erature data, along with results from the present paper. ALEX TM

refers

to a nominally 100 nm aluminum produ ed by ele tri al explosion of wire

(EEW). ASD-4isami rometri Russianprodu t, omparabletoH3[31,32℄.

Bothpowdersarenaturallypassivatedbyairandare ommer iallyavailable.

A tivated aluminum stillhave lower initialoxide ontent than the referen e

nanoaluminumbut loses5-8% ofmetalwith respe t tothe initialingredient.

Resultingideal spe i impulsedata arereported inFigure6. The

tempera-turesof therst oxidationpeakforthe A-Alfamily,dete tedbyDTA/TGA,

are signi antly lower with respe t to the behavior of mi rometri ASD-4

sample and approa h the features of the nanometri ALEX TM

powder. The

degree of metal-oxide onversion atthe end of the TGA s an in rementsfor

samplestreatedwith stronger powder a tivationandis intherange 50-70%.

Similarly, spe i surfa e area (BET analysis) is in remented with respe t

to ASD-4 and H3, but the value is still 5 to 10 times lower than ALEX TM

.

The burningrate analysis onrms ageneral

+20%

pro ess-ing. The reader should note that the benet is ve times less than the one

obtained by using anALEX TM

nano-sized aluminum [10℄.

Finally, experimental ndings suggest that only minor dieren es exist

among the a tivated powders fromthe rea tivity viewpoint. TheBET

anal-ysis identied about

±0.5m

2

_/g

variationof spe i surfa e area among the

lots, whi h is rather limited for sensible reper ussions. Similar assessments

lants are very similar. The result is more meaningful if we onsider that

heatingratesdierfromea hotherinmagnitude (10K/minforDTA/TGA,

and above 1000 K/s for propellant ombustion).

4. Con lusions

Chemi al a tivation of metal parti les is a te hnique that fosters

rea -tivity. The pro ess is able to enhan e ignition apability and in rement the

spe i surfa e area through a solutionof varying on entration. Both

mor-phology and hemi al omposition of the external surfa e are modied by

the hemi al treatment, resulting in in reased roughness and enri hed with

uorine-based ompounds. The metalli ore is unaltered, but a onsistent

aluminum depletion redu es the a tive metal ontent of about 5-7%, for

tested ases.

For the tested lots, the a tivation a omplished a general in rement of

parti le rea tivity. The spe i surfa e area was more than doubled and

DTA/TGA oxidation peak was anti ipated at the melting of the aluminum

ore. However, the degree of metal-oxide onversion at ignition was slow.

Most of the oxidation o urred at higher temperatures. Also the ballisti

hara terization onrmedthein rementedrea tivity. Uniformimprovement

of the burning rate was observed for all lots, showing negligible dieren es

among tested a tivation strengths.

Ingeneral,powderpropertiesobtained after hemi altreatmentare

simi-lartotherea tivityparametersofner uts,butarestillfarfromthebehavior

of nano-sized ingredients. In rement in burning rate an be obtained when

these advan edfuelsare usedinenergeti materials. Alsoredu tionofmetal

investiga-the depletion of the a tive metal ontent, whi h is a dire t onsequen e of

the treatment.

5. A knowledgements

The authors a knowledge the nan ial support of the European FP7

Proje tHISP (Highperforman e solid propellants for In-Spa ePropulsion),

Grant Agreement No. 262099. The authors wish tore ognize and

a knowl-edgethesigni ant ontributionoftheResear hCenterforNonConventional

Energy, EniDonegani Institute (Novara, Italy).

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1 SEM of virgin and a tivated aluminum powders.

Magni a-tion: 15,000x. . . 26

2 Granulometri distributionobtainedbylasers atteringof

sam-ples H3 and A-Al01. . . 27

3 XRD spe trum of A-Al01 powder. Aluminum onlyis dete ted. 28

4 TGA/DTAanalysisinairofH3andA-Al01powders. Sample

weight 10mg, temperatureramp 10K/min. . . 29

5 Steadyburningratevs. pressureofpropellantsembedding

a -tivated aluminum. Baseline formulation is in luded for

om-parison. . . 30

6 Ideal spe i impulse for the formulation reported in Table

3. Computations are performed under the assumptions of 70

bar ombustion pressure, expansion ratio of 40, dis harge in

( ) A-Al02 (d)A-Al03

(b)ValimetH3

Figure 4: TGA/DTA analysis in airof H3and A-Al01 powders. Sample weight10 mg,

1

10

100

Pressure, p

_c

, bar

1

10

Burning rate, r

b

, mm/s

P-Valimet

P-A-Al01

P-A-Al02

P-A-Al03

Figure5: Steadyburningratevs. pressureofpropellantsembeddinga tivatedaluminum.

are performed under theassumptions of 70 bar ombustion pressure,expansion ratioof

1 Parameters for physi al parti le hara terization. Literature

data of ALEX

TM

and ASD-4 are reported for referen e.

Spe- i surfa e areas derivefrombothBET methodand parti le

size analysis. . . 7

2 Parametersfor hemi alandthermalparti le hara terization.

ALEX TM

and ASD-4properties,availablefromtheliterature,

are reported for omparison. . . 12

3 Nominalpropellant ompositionforballisti analysis(

ρ

T M D

=

1.761g/cm

3

). Mixingwasperformedat36

◦

C; atin-based

ur-ing atalyst was used.. . . 33

4 Details of propellant hara terization. Un ertainty was

Table 3: Nominal propellant omposition for ballisti analysis (

ρ

T MD

= 1

.761g/cm

3

).

Mixingwasperformedat36

◦

C;atin-based uring atalystwasused.

Ingredient Mass fra tion Notes

AmmoniumPer hlorate 58% Coarse: 200

µ

AmmoniumPer hlorate 10% Fine: 10

µ

Metal fuel 18% Aluminum: standard ora tivated

onden e level. Propellant Powder

ρ

p

3

_∆ρ

p

r

b

= (1.28 ± 0.02) p

(0.51±0.01)

r

b

= (1.35 ± 0.04) p

(0.49±0.01)

r

b

= (1.40 ± 0.03) p

(0.48±0.01)

r

b

= (1.27 ± 0.03) p

(0.47±0.01)