安理工火工品设计原理专题讲座：Black Powder

BlackPowderLesson1IntroductionLesson2HistoryofBlackPowderLesson3SafetyLesson4HowtoMakeBlackPowderLesson5TestingYourPowderLesson6OtherExplosivesSuppliers&ReferencesKeyWords&Phrases

low-explosive 低级炸药Deflagration 爆燃Detonation 爆轰subsonicshockwaves

亚冲击波supersonicshockwaves 超冲击波Dynamite甘油炸药C-4Composition4

是一种塑料炸药，也叫高聚

物粘结炸药(PBX)PotassiumNitrate硝酸钾Ingredients 组分Oxygen 氧气Oxidizer 氧化剂IsopropylAlcohol异丙醇Flashpowder闪光粉PotassiumPerchlorate

高氯酸钾Aluminumpowder铝粉CherryBombs樱花弹Lesson1 Introduction

Anyofseverallow-explosivemixturesusedaspropellingchargesingunsandasblastingagentsinmining.ThefirstsuchexplosivewasBlackPowder,whichconsistsofamixtureofSaltPeter(PotassiumNitrate),Sulfur,andCharcoal.BlackPowder,alsoknownasGunpowder,isanexplosivethathasbeenaround,literally,forcenturies.Theexactoriginsoftheformulaarelostintime,butitisknownthattheChineseBlackPowderinweaponryatleast1,000yearsago.Technically,BlackPowderburnsbyaprocessknownasdeflagration.Thisdiffersfrom

detonation

inthatBlackPowderproducessubsonicshockwaves,asopposedtothesupersonicshockwavesproducedbyexplosivessuchasDynamite,C-4orTNT.ThismeansthatBlackPowderisbettersuitedasapropellant(suchasinfireworks,bulletsandcannons)thanblasting(suchasinconstructionordemolition).RETURNHOMELesson2 HistoryofBlackPowder

Itmayneverbeknownwithcertaintywhoinventedthefirstexplosive,blackpowder,whichisamixtureofSaltPeter(PotassiumNitrate),Sulfur,andCharcoal(Carbon).TheconsensusisthatitoriginatedinChinainthe10thcentury,butthatitsusetherewasalmostexclusivelyinfireworksandsignals.ItispossiblethattheChinesealsousedblackpowderinbombsformilitarypurposes,andthereiswrittenrecordthatinthemid-13thcenturytheyputitinbambootubestopropelstoneprojectiles.Thereis,however,someevidencethattheArabsinvented blackpowder.Byabout1300,certainly,theyhaddevelopedthefirstrealgun,abambootubereinforcedwithiron,whichusedachargeofblackpowdertofireanarrow.AstrongcasecanalsobemadethatblackpowderwasdiscoveredbytheEnglishmedievalscholarRogerBacon,whowroteexplicitinstructionsforitspreparationin1242,inthestrangeformofaLatinanagram,difficulttodecipher.ButBaconreadArabic,anditispossiblethathegothisknowledgefromArabicsources.Somescholarsattributetheinventionoffirearmstoanearly14th-centuryGermanmonknamedBertholdSchwarz.Inanycasetheyarefrequentlymentionedin14th-centurymanuscriptsfrommanycountries,andthereisarecordoftheshipmentofgunsandpowderfromGhenttoEnglandin1314.Notuntilthe17thcenturywasblackpowderusedforpeacefulpurposes.ThereisadoubtfulclaimthatitwasusedinminingoperationsinGermanyin1613andfairlyauthenticevidencethatitwasemployedintheminesof Schemnitz,Hungary(modernBanskáŠtiavnica,Czechoslovakia),in1627.Forvariousreasons,suchashighcost,lackofsuitableboringimplements,andfearofroofcollapse,theuseofblackpowderinminingdidnotspreadrapidly,thoughitwaswidelyacceptedby1700.ThefirstapplicationincivilengineeringwasintheMalpasTunneloftheCanalduMidiinFrancein1679.For300yearstheunvaryingcompositionofblackpowderhasbeenapproximately75percentSaltPeter(PotassiumNitrate),15percentCharcoal,and10percentSulfur.The SaltPeterwasoriginallyextractedfromcompostpilesandanimalwastes.DepositsfoundinIndiaprovidedasourceformanyyears.Duringthe1850stremendousquantitiesofsodiumnitratewerediscoveredinChile,andSaltPeterwasformedbyreactionwithpotassiumchloride,ofwhichtherewasaplentifulsupply.Chileannitratewasnotatfirstconsideredsatisfactoryforthemanufactureofblackpowderbecauseittooreadilyabsorbedmoisture.LammotduPont,anAmericanindustrialist,solvedthisproblemandstartedmaking sodiumnitratepowderin1858.Itbecamepopularinashorttimebecause,althoughitdidnotproduceashighaqualityexplosiveaspotassiumnitrate,itwassuitableformostminingandconstructionapplicationsandwasmuchlessexpensive.Todistinguishbetweenthem,thepotassiumnitrateandsodiumnitrateversionscametobeknownasAandBblastingpowderrespectively.TheApowdercontinuedinuseforspecialpurposesthatrequireditshigherquality,principallyforfirearms,militarydevices,andsafetyfuses.RETURNHOMELesson3 Safety

BlackPowderisdangerous!Thepowderburnsataveryhightemperature,andiseasilyignited.(Highgradepowderdoesn’tevenneedaflametoignite–itcanbesetoffbypercussion,suchasthefiringpinofapistol.)Basically,whatIamsayingisthatifyouarenotcareful,youcouldlandupwithverysevereburns,orworse.Somebasicguidelinestofollow: 1)Alwaysmixingredientsinsmallamounts.Donottrytomake10Kgofblackpowder(oranyexplosive)inonebatch.Mixingsmallamountsofpowderlimitsthepotential damageshouldanunexpectedexplosionoccur. 2)Keepyourworkplacetidy.Alwayscarefullycleanupspilledchemicals.Somematerialscanspontaneouslycombustwhenmixed(thisisespeciallytrueofnitratesandchlorates).Forthesamereason,useseparateinstruments(plasticspoons,mixingcups,etc)fordifferentchemicals.Labelyourinstrumentssothatyouknowwhatmaterialstheyhavebeenincontactwith. 3)Mixmaterialsoutdoors.Chemicalexplosivescontaintheirowninternalsourceofoxygen,andcannotbesmothered.Ifyoustartachemicalfireindoors,itcanbenearlyimpossibletoextinguish.

4)Beawareofstaticsparks.Donotusemetalinstrumentstomixorgrindmaterials.Donotstorechemicalsinmetalcontainers.Useceramicsorplasticswhereverpossible.Storechemicalsandmixturesinplasticcontainersorbags. 5)Wearsafetygoggles.Shouldtheworsthappen,skincanbegrafted.Eyescannotbereplaced.RETURNHOMELesson4 HowtoMakeBlackPowder

IngredientsBlackPowderhastraditionallyconsistedofthreeingredients:PotassiumNitrate(KNO3,alsoknownasSaltPeter),SulfurandCharcoal.TheSulfurandCharcoalprovidefuelforthereaction,whilethePotassiumNitrateprovidesOxygen.Bythemselves,CharcoalandSulfurwillburn,albeitveryslowly.Theadditionofanoxidizer(suchasKNO3)greatlyspeedsuptheburnrateofthefuel,resultinginanexplosivereaction.Thetraditionalratiooftheingredientsis15:3:2ofKNO3,CharcoalandSulfurbyweight(notvolume!).However,simplymixingthedryingredientstogetherwillnotgiveyoublackpowder.Atbest,youwillgetagreenpowderthatwilldolittlemorethanproducevastquantitiesofsmoke,andannoyyourneighbors.Inordertomakehigh-gradepowder,alittleworkisneeded. PreparingtheIngredientsThequalityoftheresultingpowderdependsonanumberoffactors.Themostimportantoftheseisbinding,whichreferstohowtightlytheKNO3ismixedinwiththeCharcoal/Sulfurmixture.Thisiswhyaloosebinding,suchasadrymix,producesaverylow-gradepowder.Thequalityofthepowderisdefinedbyitsburnrate,usuallyexpressed

incm3/s.Aburnrateofabout14cm3/sorhigherisrequiredtousethepowderasapropellant.(Also,possessionandmanufactureofpowderwithaburnrateof14cm3/sorhigherconstitutesaweaponsviolation underUSlaw,unlessyouarealsoinpossessionofanATFlicense.)Iwillpresenttwomethodsofpreparingblackpowderhere.Thefirstproducespowderwithaslightlylowerburnrate,butissafertoprepare.Thesecondcanproduceveryhighqualitypowder,butcontainsanelementofdanger.Themethodspresentedherewillgetyouaburnrateof14cm3/sorbetter,dependingonhowmuchpatienceyouhave,andthequalityofyouringredients.TheCharcoal/Sulfurmixturemustbegroundasfinelyas possible.Simplywhackingawayatyourbarbequecharcoalwithahammerisnotgoingtocutit.Thecharcoalmustbegroundintoaveryfinepowder.Commercialmanufacturersuselargemachinesknownasballmillstocrushthecharcoalandsulfur.Aballmillisbasicallyalargerotatingdrum

filledwithcharcoal,sulfurandacrushingagent,suchasleadballsorheavystones.Themillisrotatedathighspeedforupto48hoursorlonger.Theresultisaveryfinelypowderedcharcoal/sulfurmixture.(Note:forreasonswhichshouldbeveryobvious,thePotassium

Nitrateisnot

mixedinwiththefuelduringthemillingstage,unlessyouwanttobepickingbitsofyourballmilloutofthewallsofyourfactory.)BallMillsareveryexpensive,anditisunlikelythattheaveragehobbyistwillbeabletoaffordone.Therearealternatives,however.Oneistosimplybuythecharcoalinapowderedform.Thereareseveralmailordercompaniesthatwillprovidepowderedcharcoal.(Seethelistofsuppliersattheendofthisarticle).Theotheralternativeistofashionaballmillofyourown,ifyouhappentobeahandyman.Or,youcouldsimplybuyacheapgem-polishingtoymillfromyourlocalWal-Mart,andusekidsmarbles,orheavydecorativestonesasacrushingagent. Youwillhavetorunthemillcontinuouslyforatleast72hourswiththismethod,however.Assumingthatyouhaveapowderedcharcoal/sulfurmixtureintherightquantities,howdoyougettheKNO3tobindtothemixture?ThesolutionistoemployausefulpropertyofPotassiumNitrate–itissolubleinwater.Charcoalandsulfur,ontheotherhand,arenotsolubleinwater.Theywill,however,absorbKNO3fromwaterundersuitablecircumstances.Theadditionofcoldalcoholtothemixwillhavetheeffectofsuddenlyleachingthewateroutofthemixture,leavingjustthesaltbehind,hopefullytightlyboundtothefuel. Method1–BoilingRequirements: Skillet,stovetop(preferablyoutdoors!),plasticstrirrer,750mlofIsopropylAlcohol,householdsieves,coffeefilters.Therecipeforproducingblackpowderusingthismethodisasfollows(adjustquantitiesasdesired,butremembertosticktotheratio).Beforeyoustart,havea750mlbottleofrubbingalcoholchilledinafreezerforatleast24hours. (Youcanpurchaserubbingalcohol,alsoknownasIsopropylAlcohol,frommostanydrugstoreorsupermarket). 1)Mix30gramsofpowdered

charcoalwith20gramsofpowderedsulfur,asdescribedabove. 2)Usingadeepskillet,bringaboutthreeorfourcupsofwatertoboil.Stirin150gramsofKNO3.KeepstirringuntilthePotassiumNitrateiscompletelydissolved.Addwaterasnecessary,buttrynottoover-waterthemixture. 3)Slowlysiftinthecharcoal/sulfurmixture.Themixturewilltendtofloatontopofthewater,soyouwillhavetoagitatetheslushwithaspoonorawhisk.Keepstirringuntilyougetawet,grayishsludge.Thiscouldtakeawhile,sotakeyourtimeandbecareful.

Don’tletanyofthemixtureslopoutoftheskilletontothehotstove-top,oryouwillmostlikelystartafire. 4)Oncethesludgeisuniformlymixed,removetheskilletfromthestove.Pourinthechilledalcohol,andstir.Keeppouringandstirringuntilthesludgeiscoolenoughto touch. 5)Pourthesludgeintoacoffeefilterplacedinasieveoveraplasticcontainer.Allowthewater/alcoholtodrainoutuntilthesludgeisdryenoughtoleaveanimpressionwhenyoupressintoit. 6)Usingafinesieve,pressthesludgethroughthesieveontoalargepieceofcardboardorblottingpaper.Thisshouldproducefinegranulesofpowder.Takeyourtime,evenlyspreadingthegranulesontothepaperorcardboard. 7)Allowthegranulestodryindirectsunlightforat least24hours.Whendry,pourthegranulesthroughafinersievetoremoveanyfinepowderfromthegranules.Thisfinepowder(knownasmealpowder)isnotusefulforfirecrackersorpropellants,butcanbeusedtomakefusesorfountains.Youshouldnowhavereal,honest-to-goodnessBlackPowder.Congrats. Method2–AgitationThismethodisverysimilartothatdescribedabove,butdiffersinthemannerinwhichtheingredientsaremixed.Becauseituseselectricalequipment,itisconsiderablymoredangerousthanthepreviousmethod,butcanproduceveryhighqualitypowder.Requirements: Electrickitchenblender,750mlofIsopropylAlcohol,householdsieve,coffeefilters. 1)Pour3or4cupsofboilingwaterintotheblender.Slowlyadd150gramsofKNO3.Covertheblender,and agitateatmediumspeedforabouttenminutes. (Note–itisadvisabletouseanextensioncordtostarttheblenderfromasafedistance.Again,thisshouldbedoneoutdoors!) 2)Slowlymixin50gramsofcharcoal/sulfurmixture.Thisshouldbedonebyturningofftheblender,pouringinasmallamountofthemixture,restartingtheblenderandmixinguntilthecharcoal/sulfuriscompletelywet.Repeatuntilallthefuelhasbeenaddedandthoroughlymixed.(Takeyourtime–remember:hastekills!) 3)Lettheblenderrunathighspeedforabout15minutes.Slowlypourinthealcoholwhiletheblenderisrunning.Youshouldheartheblenderslowdownasthemixturesolidifies.Addmorealcoholuntilthemixtureiscooltothetouch. 4)Followsteps5through7frommethod1.

RETURNHOMELesson5 TestingYourPowder

Inordertotesttheburnrateofyourpowder,allyouneedisastopwatchandasodacan.Thankstothemagicofthemetricsystem,itturnsoutthat1ml=1cm3.Sodacansareusuallymarkedwiththevolumeinml(theaveragecanis340ml).Youmaynotwanttouseanentirecan,however,asthatwouldbeawaste.Mostsupermarketssellsodainhalf-sizecans(suchasyouusuallygetonairliners).Or,youcouldsimplycutafullsizedcanusingapairofmetalshears,andcalculatethevolumeofthecan.(Forthoseofyouwhosleptthroughmathathighschool,theformulaisv=h*Pi* r2.Remembertousemetric

units.Inotherwords,measuretheheightanddiameterofthecanincentimeters,notinches,milesorfurlongs,orwhateverelseyouYankshavegotstuckwith.)Now,fillthecantothebrimwithpowder.Donotcoverthecan!Oneword–shrapnel!Insertafuse(youcanusuallybuyso-called‘safetyfuses’fromasupermarketaroundthe4thofJuly,orNewYears.Also,fireworksretailersalmostalwayscarrylengthsofsafetyfuse.Ifyouaredesperate,simplyinsertamatchintothecan,withthematch-head Justunderthesurfaceofthepowder.)Lightthefuse,waitforthepowdertostartburning,andtimetheburnwiththestopwatch.Dividethevolumeofpowderbythetimeittakestoburncompletely,andyouhaveyourburnrate.

ThingsthatgoBang!Sonowyouhaveblackpowder.Whatdoyoudowithit?Shortanswer–youmakeitexplode,ofcourse!Thisisachievedbyconfiningthepowderinsideacontainerandinitiatingapressure-feedbackloop.Forthephysics-impaired,thisishowitworks:theburnrateofblack powderisdirectlyproportionaltothesurroundingpressure.Themorethepressureincreases,thefasterthepowderburns.Ifthepowderburnsinaconfinedspace,itwillreleaselargequantitiesofgas,whichinturnincreasetheinternalpressure,whichincreasestheburnrateofthepowder,whichreleasesmoregas….well,yougettheidea.Thefeedbackloopcontinuesuntiltheinternalpressureburststhecontainer,resultinginalargebang.Thewholeprocesstakesplaceinamatterofmilliseconds,ifyourpowderisofsufficientquality.Thisiswhyweusegranulatedpowderforfirecrackers–granulesmeansmoresurfacearea.Moresurfaceareameansthatthehotgasestravelingthroughthecontainercanignitemorepowder, morequickly.So,whatdoweuseforacontainer?Allthoseofyouwhosaid‘metalpipes’or‘glassbottles’,pleasepickupyourthingsandgetthehelloutofmyclassroom.Anyonewithtwobraincellstorubtogethershouldrealizethatwhenametalorglasscontainerbursts,theairwillsuddenlybefilledwithverytinypiecesofglassormetal,travelingatspeedsofseveralhundredmeterspersecondinalldirections.This,boyandgirls,iswhatwecallshrapnel,

andouraimistoavoidit,unlessyouwanttoenduplooking likeapieceofSwisscheese.Firecrackercontainersaremadeofcardboard,orsoftplastic.Notonlyisapieceofflyingcardboardfarlessdangerousthanasupersonicpieceofsharpmetal,butcardboardandplasticcontainerstendtobeconsumedbytheheatoftheexplosion,leavingevenfewerpotentiallydangerousmissilestoflyaround.Thesupplierslistedbelowwillcarrypre-madecardboardtubes,withplugsthataregluedintotheendstoformatightlycontainedtube.Ifyouhappentobeimpatient,youcanprobablyfindsomethingaroundyourhousethatmightdothetrick.Twofairlycommonhouseholditemsthatyoucouldusearethesoftplasticcontainersthat35mmfilmisusuallysoldin,orthesoftplasticcontainersinwhichyourlocalpharmacistusuallydispensesdrugs.(Bytheway–ifyourlocalpharmacistisaguynamed‘Jim’whohangsarounddarkalleys,youshouldn’tbeexperimentingwithexplosives.Kapish?)Tostartwith,makeasmallholeinthetopofthecontainer.Punchordrillaholeabout2to3mmindiameterinthetopofthecontainer.Placeawoodentoothpickinthe whole(you’llfindoutwhylater.)Fillthecontaineraboutone-thirdtoone-halfwithgranulatedblackpowder,andgluethetopbackon.Useastrongglue,likeWelder’sall-purpose,orahotgluegunifyouhaveone.Regularmodelcementgluewillnotbestrongenoughtokeepthetopinplaceduringtheexplosion.Now,weturntotheonesupplythatnopyroshouldbewithout–ducttape.Cutalongstripoftape,longenoughtocompletelycoverthecontainerfromtoptobottomandbackagain.Thisiswherethetoothpickcomein–pushthe tapeslowlyoverthetoothpickontothetopofthecontainer.Thetoothpickwillmarktheplacewherethefusewilllaterbeinserted.Repeattheprocessuntilthecontaineriscompletelycoveredwithtape.Thepurposeofthetapeistwo-fold:first,itstrengthensthecontainerallowingmorepressuretobuildupbeforeitburstsandsecondly,ittrapsanypiecesofthecontainerthatmightotherwisehaveatendencytobeejectedfromtheexplosion.Whiletheglueisdrying,removethetoothpickandinsertthefusethroughtheholeleftbehind.Thefuseshouldfitsnugly.Whentheglueisdry,takethewholedeviceoutside,placeontheground,lightthefuseandgetoutoftheway.RETURNHOMELesson6 OtherExplosives

FlashPowderBlackpowderisnottheonlyexplosiveagentoutthere–thereareliterallyhundreds,allwithdifferentusesandcharacteristics.Flashpowderisonesuchmaterial.Itwasoriginallyusedtoproducethebrightflashforthoseold-timephotographs.Flashpowderhassomeprosandconsoverblackpowder:Pros:Flashpowderismuch,mucheasiertomake.ItalsoproducesfarmoreheatandsoundthanaBPexplosion.Cons:Flashpowderishighlyunstable.Itcaneasilybesetoffbyfrictionalone.ItalsoproducesafarmorepowerfulexplosionthanBP.Ifyouaredumbenoughtoholda containerofBPinyourhandwhileitexplodes,youwilllandupwithseverelyburntfingers.Ifyourepeattheexperimentwithflashpowder,youwilllandupwithnofingersatall.I’mnotkidding.Ihavepersonallyseen40gramsofflashpowderinacherrybombleaveacraterahalffootdeepinmybackyard. Ingredients Thereareseveralcompositionsofflashpowder.Thesafest(relativelyspeaking)isPotassiumPerchlorate(KClO4)andAluminumpowder.Thisproducesapowderwhichisrelativelystable,butslightlylesspotentthantheothercompositions.FlashpowdercanalsobemadefromPotassiumChlorateandAluminumpowder.Thi