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Improvedgreen-light-emittingpyrotechnicformulationsbasedontris(2,2,2-trinitroethyl)-borateandboroncarbideThomasM.
Klapo¨tke,*aBurkhardKrumm,aMagdalenaRusanaandJesseJ.
Sabatini*bGreen-light-emittingpyrotechniccompositionsbasedontris(2,2,2-trinitroethyl)borate(TNEB)andboroncarbidehavebeeninvestigated.
Thebestperformingformulationswerefoundtobeinsensitivetovariousignitionstimuli,andexhibitedveryhighspectralpuritiesandluminositiescomparedtopreviouslyreportedgreen-light-emittingformulations.
Traditionalgreen-light-emittingpyrotechnicformulationsrelyonacombinationofbariumcompoundsandchlorinedonorstoachieveasuitablegreen-light-emittingspecies.
1Inthesemixtures,bariumnitrateiscombinedwithachlorinedonorsuchaspoly(vinyl)chloridetoformmetastablebarium(I)chlorideasthegreen-light-emittingspecies.
1Spectralpuritiesofbarium-basedgreen-light-emittingilluminantsaretypicallyinthelow-to-high60%range.
Thisrelativelylowspectralpurityisaresultoflargeamountsofwhite-light-emittingincandescentparticles(i.
e.
MgO,BaO)formedduringthecombustionofagivenformulation.
Unfortunately,bariumcompoundsaresuspectedcardiotoxinsandhavebeenlinkedtohazardsassociatedwithoccupationalhealth.
2Furthermore,thereisconcernthatthecombustionofchlorinedonorssuchasPVCleadstotheproductionofsignificantamountsofcarcinogenicmaterialssuchaspoly-chlorinatedbiphenyls(PCBs),polychlorinateddibenzodioxins(PCDDs),andpolychlorinateddibenzofurans(PCDFs).
3Thus,theremovalofbarium-andchlorine-containingmaterialsfromgreen-light-emittingpyrotechnicformulationsisofhighinterestin''greening''thisclassofgreen-light-emittingpyrotechnicformulations.
In2011,Sabatinietal.
developedabarium-andchlorine-freegreen-light-emittingpyrotechnicformulationbyburningamixtureofpotassiumnitrate/boroncarbide/epoxybinder.
4Green-light-emissionoccurredduetotheformationandemissionofmetastableborondioxide(BO2)asopposedtothetraditionalbarium(I)chloridespecies.
Whilethismixturegivesdecentgreen-light-emissionandisveryinsensitivetoimpactfrictionandelectrostaticdischarge,ithasarelativelylowspectralpurity.
Lowspectralpuritiesareaconsequenceof"washingout"oftheflamecolour.
Thisphenomenonlikelyoccurredduetothepresenceofhighlevelsofpotassiumnitrate,whichproduceswhite-light-emittingKOH.
5Therefore,itwasbelievedthatreplacementofpotassiumnitratewithametal-freeoxidizerwouldimprovethecolourpropertiesthroughtheminimizationofincandescentparticleemission.
Althoughitwasinitiallypostulatedthatmixturesofammoniumnitrate/boroncarbideorammoniumdinitramide/boroncarbidemayresultinhighqualitygreen-light-emission,5,6attemptstoproducegreenlightbythesemeanswereunsuccessful.
SincetheproductionofmetastableBO2favoursgreen-light-emission,attentionwasthenturnedtoaboron-containingoxidizertomaximizethequalityofagreen-light-emittingflamebasedonboroncarbide.
Tris(2,2,2-trinitroethyl)-borate(TNEB),whichwassynthesizedpreviously,7wasconsideredtobethecompoundofinterestinthisstudy.
TNEBcontainsbothaboroncentreandtrinitroethylenergeticligands.
Withanoxygenbalanceof+13.
1,TNEBwasdeterminedtobeasuitableoxidizingmaterialforthisresearchinvestigation.
Thegreen-light-emittingformulationcontainingpotassiumnitrateandboroncarbidereportedbySabatinietal.
4wasreinvestigatedwiththehereinusedequipmenttoestablisharelevantdatapoint(Table1).
Thisgreen-light-emittingformulationhadaspectralpurityof69%(Table2).
ItshouldbenotedthatTNEB(Fig.
1)isamoisturesensitivematerial,owingtothehighlyreactivenatureandthevacantp-orbitaloftheboroncentre.
Whensynthesized,thematerialdecomposesafterseveralTable1Formulation1FormulationKNO3[wt%]B4C[wt%]Epon828/Epikure3140[wt%]183107aDepartmentofChemistry,EnergeticMaterialsResearch,Ludwig-MaximilianUniversityofMunich,Butenandtstr.
5-13,D-81377Munich,Germany.
E-mail:tmk@cup.
uni-muenchen.
de;Fax:+4989218077492;Tel:+4989218077491bPyrotechnicsTechnologyandPrototypingDivisionUSArmyRDECOM-ARDEC,PicatinnyArsenal,NJ08706-5000,USA.
E-mail:jesse.
j.
sabatini.
civ@mail.
mil;Fax:+1-973-724-7375Received18thJune2014,Accepted5thJuly2014DOI:10.
1039/c4cc04616awww.
rsc.
org/chemcommChemCommCOMMUNICATIONdaysofstorage.
Whenpreparingpyrotechnicmixturescontainingthisoxidizer,itisrecommendedthatnon-basicmaterialsbeusedtopreventanyundesiredside-reactionsfromoccurringwithTNEB.
Therefore,theuseofepoxy-basedbindersystemsthattypicallyemploypolyamine-basedcuringagentsisnotrecommended.
TohelpminimizethedecompositionofTNEB,andtoassistinprovidingsealant-likepropertiesfortheTNEB-containingformulations,paranwasaddedtotheformulationsinlieuofthepolyamine-basedbindersystem.
MixingallsolidingredientsinliquidparanoeredamoistureresistantqualitytotheformulationsdetailedinTable3.
Thepresenceofmagnesiuminformulations2and3wascriticalinordertomaintainahighcombustiontemperature.
Green-light-emissionwasnotobservedwhenmagnesiumwasomittedfromtheseformulations.
TheperformancesofbothmixturesandtheirenergeticandthermalpropertiesaresummarizedinTable4.
Formulations2and3burnedwithlittlesmoke,andyieldedanintensivegreenflame(Fig.
2).
Theseformulationsrevealrespectivespectralpuritiesof86%and85%,whichexceedthespectralpurityofformulation1duetotheabsenceoflargequantitiesofpotassium-basedwhite-light-emission.
Theluminousintensitiesofformulations2and3areappreciablyhigherthantheluminosityobservedinformulation1,aphenomenonduetothepresenceofmagnesiumintheformerformulations.
Formulation2wasobservedtobethebestoftheTNEB-basedformulationstestedonthebasisoftheperformanceobtained.
Formulation2notonlyhadanequivalentburntimetoformulation1,butitalsosurpassedthelatterformulationinallperformancecategoriesbywidemargins.
Furtherpictorialevidenceofthesuperiorspectralpuritiesofformulations2and3isprovidedintheCIE1931chromaticitydiagram(Fig.
3).
Formulations2and3werefoundtorespondtovariousignitionstimuli,eachhavinganimpactsensitivityhigherthan40Jandafrictionsensitivityinexcessof360N.
Therespectivedecompositiontemperatureswere1701Cand1681C.
Insummary,agreen-light-emittingpyrotechnicformulationwithhighperformanceandspectralpurityhasbeenobtainedbymeansofreplacingpotassiumnitratewithTNEBinthepresenceofboroncarbide,magnesium,andparanwax.
Inparticular,for-mulation2exceedstheperformanceofpotassiumnitrate-basedformulation1inallcategories,whileformulation3yieldsthehighestoverallluminosity.
Theaforementionedcompositionsareveryinsensitivetoimpactandfriction.
Althoughfurtherstudyisneededtoaddresspotentialconcernsassociatedwithmoisturesensitivity,theresearchisofpotentialinteresttothoseinthepyrotechnicscommunityconcernedwithfindingenvironmentallyfriendlyalternativestobarium-andchlorine-basedgreen-light-emittingpyrotechnicsofhighluminosityandspectralpurity.
Caution!
Tris(2,2,2-trinitroethyl)borateisanenergeticmaterialandformulations1–3areenergeticformulationswithhighsensitivitytowardsheat,impactandfriction.
AlthoughnoTable2Colorpropertiesofformulation1FormulationBTa[s]DWb[nm]SPc[%]LId[cd]LEe[cdsg1]165606925250aBT=Burntime.
bDW=Dominantwavelength.
cSP=Spectralpurity.
dLI=Luminousintensity.
eLE=Luminouseciency.
Fig.
1Structureoftris(2,2,2-trinitroethyl)borate.
Table3Formulations2and3TNEB[wt%]B4C[wt%]Mg[wt%]Paran[wt%]27910473751087Table4Colorperformancesandenergeticandthermalpropertiesofformulations2and3FormulationBTa[s]DWb[nm]SPc[%]LId[cd]LEe[cdsg1]ISf[J]FSg[N]Tdech[1C]27561865058344043601703456285895934404360168aBT=Burntime.
bDW=Dominantwavelength.
cSP=Spectralpurity.
dLI=Luminousintensity.
eLE=Luminouseciency.
fIS=Impactsensitivity.
gFS=Frictionsensitivity.
hTdec=Temperatureofdecomposition.
Fig.
2Formulation2(left)andformulation3(right)atmid-burn.
Fig.
3CIE1931chromaticitydiagramofformulations1–3.
CommunicationChemCommincidentsoccurredduringpreparationandmanipulation,additionalproperprotectiveprecautionslikefaceshield,leathercoat,earthedequipmentandshoes,Kevlargloves,andearplugsshouldbeusedwhenundertakingworkwiththesecompounds.
8TNEBwassynthesizedaccordingtotheliteratureprocedure.
7Boroncarbide,amorphousboron,potassiumnitrate,andparanwerepurchasedfromAldrichandwereusedasreceived.
Thepyrotechnicalcompositionswerepreparedbygrindingallsub-stancesinamortar.
Themixturewasthenintroducedslowlyintowarmliquidparan.
Aftercoolingtoroomtemperature,themixturesweregrindedagain.
Pelletsof0.
6geachwerepressedusingaconsolidationdeadloadof2000kg.
Thepelletsweredriedovernightatambienttemperature.
Thecontrolledburnwasfilmedusingadigitalvideocamerarecorder(SONY,DCR-HC37E).
Theperformanceofeachcompositionwasevaluatedwithrespecttocoloremission,smokegeneration,andtheamountofsolidresidues.
SpectrometricmeasurementswereperformedusingaHR2000+ESspectrometerequippedwithanILX511BlinearsiliconCCD-arraydetectorandincludedsoftwarefromOceanOpticswithadetector-sampledistanceof1meter.
Thedominantwavelengthandspectralpurityweremeasuredbasedonthe1931CIEmethodusingilluminantCasthewhitereferencepoint.
Luminousintensitiesandluminousecienciesweredeter-minedusingpelletsof0.
6geach.
Fivesamplesweremeasuredforeachformulationandallgivenvaluesareaveragedbasedonthefullburnofthemixture.
DecompositionpointsweremeasuredusingaLinseisPT10DSCatheatingratesof51Cmin1.
9Theimpact10andfriction11sensitivitywasdeterminedusingaBAMdrophammerandaBAMfrictiontester.
ThesensitivitiesofthecompoundsareindicatedaccordingtotheUNRecommendationsontheTransportofDangerousGoods(+):12impact:insensitive440J,lesssensitive435J,sensitive44J,verysensitiveo4J;friction:insensitive4360N,lesssensitive=360N,sensitiveo360N480N,verysensitiveo80N,extremelysensitiveo10N.
FinancialsupportofthisworkbytheLudwig-MaximilianUniversityofMunich(LMU),theU.
S.
ArmyResearchLaboratory(ARL)undergrantno.
W911NF-09-2-0018,theArmamentResearch,DevelopmentandEngineeringCenter(ARDEC)undergrantno.
W911NF-12-1-0467,andtheOceofNavalResearch(ONR)undergrantno.
ONR.
N00014-10-1-0535andONR.
N00014-12-1-0538isgratefullyacknowledged.
TheauthorsacknowledgecollaborationswithDrMilaKrupka(OZMResearch,CzechRepublic)inthedevelopmentofnewtestingandevaluationmethodsforenergeticmaterialsandwithDrMuhamedSuceska(BrodarskiInstitute,Croatia)inthedevelopmentofnewcomputationalcodestopredictthedetonationandpropulsionparametersofnovelexplosives.
WeareindebtedtoandthankDrsBetsyM.
RiceandBradForch(ARL,Aberdeen,ProvingGround,MD)formanyinspireddiscussions.
TheCusanus-werkisgratefullyacknowledgedfortheawardofaPhDscholarship(M.
Rusan).
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