37Chemical ExplosivesandRocket PropellantsWalter B. Sudweeks, * FelixF. Chen, **andMichael D. McPherson**PART I. CHEMICALEXPLOSIVESINTRODUCTIONThe average citizen in today's world giveslittlethought totheimportant rolethat com-mercial explosivesplayinour livesandhowtheir use is linked to our standard of living andour way of life. Explosives provide the energyrequired to give us access to the vast resourcesofthe earth for the advancement ofcivilization.Tomaintain our standard oflivingintheUnitedStates, every day187,000 tons of con-crete are mixed, 35million paper clips arepurchased, 21millionphotographsaretaken,usinglargequantities of silver,80 poundsofgoldareusedto fill 500,000cavities, and3.6million light bulbs are purchased. It takes*Consultant, Part I, Chemical Explosives . Theauthorwishestoacknowledgethat this sectionisanupdateof the corresponding material in the tenth editionauthoredbyBoydHansen.**Aerojet Propulsion Division. Part II, RocketPropellants.1742more than 40 different minerals to make atelephone, and35 tomakea colortelevision.Eveneverydayproductssuchastalcumpow-der, toothpaste, cosmetics, and medicinescontainminerals, all of whichmust be minedusingchemical explosives. IWithout explosives the steel industry andourentiretransportationsystemwouldnot bepossible. The generation ofelectricity has beenlargelydependent oncoal, andcoal miningtoday is still the largest consumer of industrialexplosives. Rockquarryingforroadbuildingand excavations for skyscrapers, tunnels,roads, pipelines, and utilities are direct benefi-ciaries of the labor-saving use of explosives.COMMERCIALEXPLOSIVESMARKETThe use of commercial explosives in the UnitedStates was fairly constant over the past decade,averaging between 2 to 3 million tons per year.Figure 37.1 indicates explosives usage byyear as reported by the u.s. Geological SurveyI=Coalmining[TIQwmyingandnonmctll1mining0Metalmininga:IConstructionworkOtherusesIFig.37.1.SalesforconsumptionofU.S.industrialexplosivesfrom1991to2000.(Kramer,DeborahA.,UnitedStatesGeologicalSurvey,ExplosivesStatisticsandInformation,MineralsYearbook2000,andtheInstituteofMakersofExplosives.)3,5003.000~ :zo2,500.-~ ~2,000~ 0 ~1,500~ ;:)@1.000to-500 0199419951996199719981999YEAR2000200120022003o :::E:m s:c:;> ....m X -g....o VI 2:C ::co (")~ m -I-g::co -gm ........> 2:-IVI~ ...,~ w1744 KENTANDRIEGEL'S HANDBOOKOF INDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYTABLE37.1 Industrial Explosives and Blasting Agents Sold in theUnited States byState and Class(Metric Tons)2002 2003Fixed High Explosives FixedHigh ExplosivesOther Blasting Other BlastingHigh Agents and High Agents andState Permissibles Explosives Oxidizers Total Permissibles Explosives Oxidizers TotalIndiana 3 1,130 220,000 221,000 38 1,070 204,000 205,000Kentucky 780 1,990 312,000 315,000 439 1,410 264,000 266,000Pennsylvania 81 1,810 117,000 119,000 71 1,490 127,000 128,000Virginia 163 1,670 159,000 161,000 106 3,300 141,000 145,000West Virginia 19 1,170 363,000 364,000 121 719 331,000 332,000Wyoming 39 528 272,000 273,000 2,420 231,000 234,000Others 270 29,799 1,025,141 1,055,544 291 25,095 953,198 978,351Total 1,360 38,100 2,470,000 2,510,000 1,070 35,500 2,250,000 2,290,000Note: Datarounded; may notadd up to total shown.Source:IME.(USGS) and the Institute of Makers ofExplosives (IME) from 1994 to 2003.2,3 Figure37.1alsoseparatesthevolumesbyindustryuse. The open-pit coal mining industry contin-uestobethelargest user,asithasbeenformany years. Table 37.1 shows the commercialexplosiveusage by sevenleading states for2002and20m? Intheyear 2003, the fourstates consuming the most explosives (indecreasing order) were: West Virginia,Kentucky, Wyoming, and Indiana, all coal min-ing states. The coal market is also slowlymak-ing a shift fromthe eastern states to the westernstates withlower BTU, butmoreimportantly,lower sulfur coal. Through the 1990s thesparsely populatedstateof Nevadarankedinthe top ten states using commercial explosives.This reflected the growth of large volume goldmining operations in North America. Many ofthe smaller underground gold mines weretransformed into large open-pit operationsusing efficienciesof scale to overcometheoverall lower gradeof ore, thesame transfor-mations that other metal mines had madedecades before. Along with this change in min-ing style came a conversion from small diame-terpackagedexplosives suchasdynamite tolarge, bulkexplosive loadingsystemsusingemulsions and ammoniumnitrate/fuel oil(ANFO).CHEMISTRYOF COMBUSTIONANDEXPLOSIONFor a simple understandingof explosives it ishelpful to compare an explosive reaction withthe more familiar combustion or burningreaction. Three components are needed tohave a fire: fuel, oxygen, and a source of igni-tion. Theprocessof combustionisbasicallyanoxidation-reduction (redox) reactionbe-ween thefuel andoxygen from theair. Onceinitiated, this reactionbecomes self-sustain-ing and produceslarge volumes of gasesandheat.Theheat givenofffurther expandsthegasesand providesthestimulusfor thereac-tion to continue.The burning reaction is a relativelyslowprocess, dependinguponhowfinelydividedthe fuel is, that is, the intimacyofcontactbetweenthefuel andtheoxygenintheair.Because burning isdiffusion-controlled, themore intimately the fuel and oxygen aremixed, the faster theycanreact. Obviously,the smaller the particles of fuel, the faster thecombustioncan occur.Another result of the fineness or particlesizeof thefuel isthecompletenessor effi-ciencyof thereaction. Inacomplete com-bustionall the fuel elements are oxidizedtotheirhighest oxidationstate. Thus, wood,CHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1745OXIDIZERFig. 37.2. Anexplosiontriangle.Oxidation-Reduction- gases + heat(fast)N--_..... SOURCEOFIGNmON FUELIt shouldbe notedthatanexplosiondiffersfrom ordinary combustionin two very signifi-cantways. First, oxygenfromthe airisnot amajorreactant in theredoxreactionsof mostexplosives. The source ofoxygen(or otherreducible species) needed for reaction with thefuel-theoxidizer-maybepart of thesamemoleculeas thefuelora separateintermixedmaterial. Thus an explosive may be thought ofas merely anintimate mixture of oxidizer andfuel. This degree of intimacy contributes to thesecond significant difference between anexplosion and normalcombustion-the speedwith which the reaction occurs.Explosives inwhichthe oxidizer andfuelportions are part ofthe same molecule arecalledmolecular explosives. Classical exam-ples of molecular explosives are 2,4,6- trinitro-toluene (TNT), pentaerythritol tetranitrate(PETN), andnitroglycerin (NG) or, more pre-ciselyglycerol trinitrate. Thechemical struc-tures of these explosives are shown in Fig. 37.3.Ascanbeseenin thestructures, theoxidizerportions of the explosives are the nitro (-N02)groups in TNT and the nitrate (-ON02) groupsin PETN and NG. The fuel portions of all threeexplosives are the carbon and hydrogen (C andH) atoms. Comparison of the ratios of carbontooxygenintheseexplosives(i.e., approxi-mately1 : Ifor TNT, approximately1: 2 forPETN, and1: 3 for NG) shows that TNTandPETNaredeficient inoxygen; that is, thereis insufficient oxygen present inthe mole-culetofullyoxidize thecarbon andhydro-gen. Consequently, products such as carbonmonoxide, solidcarbon(soot), andhydrogenareproduced, aswell as carbondioxideandwater vapor. Prediction of the exact products ofbeingmainlycellulose , andgasoline , beinggenerallyahydrocarbon(e.g. , octane), pro-duce primarily carbon dioxide and watervapor upon complete combustion. Onceiniti-ated these burning reactions give off heatenergy,whichsustainsthereactions. Heat isreleasedbecausethe oxidized productsof thereaction are lower inenergy (more stable)than the reactants. The maximumpotentialenergy release can be calculated fromtherespecti ve heats of formationof the productsand reactants. Actual heats of combustioncanbemeasuredexperimentallybycausingthereactiontooccur inabombcalorimeter.The calculatedenergy values for the abovereactions are - 3,857 cal/gforcelluloseand- 10,704 cal/g for octane, respectively.In the case of an inefficient burn, some lessstableorhigher-energyproductsareformedsothat theresultantheat energygivenoff islower thanthat forcompletecombustion. Inthe above examples inefficient combustioncouldresult fromlack of oxygenaccessibil-ity, producing carbonmonoxide or even car-bon particles instead ofcarbon dioxide. Asmoky flame is evidenceof unburned carbonparticles and results frominefficient com-bustionwhere fuel particlesaresolargeorsodense that oxygen cannot diffuse totheburningsurface fast enough. Ifthis ineffi-ciency is great enough, insufficient heat isgivenoff tokeepthereactiongoing, andthefire willdieout.All chemical explosive reactions involvesimilar redoxreactions; sotheaboveprinci-ples ofcombustioncanhelp illustrate, inavery basic way, the chemistry involved inexplosions. As in a fire, three components(fuel, oxidizer, ignition source) are needed foran explosion. Figure 37.2 shows an explosiontriangle, whichissimilar tothefire triangle.Ingeneral , theproducts of anexplosionaregasesand heatalthoughsomesolid oxidationproducts maybeproduced, depending uponthe chemical explosive composition. As innormal combustion, thegasesproducedusu-allyincludecarbondioxideandwatervaporplus other gases such as nitrogen, againdepending upon the composition of the chem-ical explosive.1746 KENTANDRIEGEL'S HANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYTNTPETNNGON02CH3ICH2-0N02CH202NIQrN02II2NO-H2C-C-eH2-0N02ICH-ON02H HCH2IIN02ON02 CH2-0N02Fig. 37.3. Chemical structureof threemolecular explosives.explosioniscomplex,especially fortheoxy-gen-deficient explosives, because the ratios ofcOz, CO, HzO, andHz will vary, dependingupon reaction conditions (explosivedensity,degree of confinement of the explosive, etc.).4,SThe followingequations showtypical idealreaction productsalongwithcalculated heatsof reaction for these molecular explosives:C7HsN306~ 1.5COz+ 0.5CO + 2.5HzOTNT +1.5Nz +5C+1290 callgCsHgN401Z~ 4COz +4HzO +2Nz +CPETN +1510 callgwhat isneededfor complete combustionofthe fuel elements) or oxygen deficiency(compared to the amount required forcomplete combustion). It is expressed aseither apercentage or adecimal fractionofthe molecularweight of the oxygen in excess(+ ) or deficiency (- ) divided by the molecu-larweightof theexplosiveortheingredientbeing considered. Individual componentsof an explosive mixture have O.B. valuesthat may be summed for the mixture.Shownbeloware the O.B. calculations forAN and FO:FOMol. wt. = -14n+(112)(32)O.B. = 80 =+0.20- (3n/2)(32)O.B.= 14n =-3.43Mol. wt. =32 ANMol. wt. = 80From the O.B. values, one can readilydetermine theratioof ingredients togiveazero O.B. mixture for optimum efficiency andenergy.Thus theweight ratiofor ANFOis94.5 parts of AN and 5.5 parts of FO(94.5X0.20 = 5.5 x3.43).For themolecular explosivesshownprevi-ously, the respective oxygen balances are:TNT, -0.74;PETN, -0.10; and NG, +0.04.Thus, NG is nearly perfectly oxygen-balanced;C3HsN309~ 3COz +2.5HzO +1.5NzNG +0.250z+1480 callgExplosives inwhichtheoxidizer andfuelportions come fromdifferent molecules arecalled compositeexplosives becausethey area mixture of two or more chemicals. A classicindustrial example is a mixture of solidammoniumnitrate (AN) andliquidfuel oil(FO). The common designation for this explo-sive is the acronym, ANFO. The oil used (typ-ically#2diesel fuel) is added insufficientquantity toreact withthe availableoxygenfromthe nitrate portion of AN. The redoxreaction of ANFO is as follows:3NH4N03+-CHz-AN FO~ COz +7HzO+ 3Nz +880 callg"Oxygen balance" (O.B.) is the termappliedtoquantifyeithertheexcessoxygenin an explosive compound or mixture (beyondCHEMICALEXPLOSIVES ANDROCKET PROPELLANTS 1747PETNisonlyslightlynegative; but TNTisvery negative, meaningsignificantly deficientinoxygen. Therefore, combinations of TNTand AN have been employed to provide addi-tional oxygen for the excess fuel, as, forexample, in theAmatols developed bytheBritish in World War 1.6Modemcommercial explosivesreact inavery rapidandcharacteristicmannerreferredto as a detonation. Detonation has beendefined as a process in which a shock-inducedsupersonic combustion wave propagatesthrough a reactive mixture or compound. Thishigh pressure shock wave compresses thereactive material in contact with it resulting inrapid heating of the material, initiation ofchemical reaction, andliberation of energy.This energy, intum, continues todrivetheshockwave. Pressure inadetonation shockwave may reach millions of pounds per squareinch. The suddenpressure pulse shocks theexplosive material as it passesthrough, caus-inganearlyinstantaneouschemical reactioninthebodyoftheexplosive. Onceinitiated,molecular explosivestendtoreachasteady-state reactionwith a characteristicdetonationvelocity. Composite or mixture explosivesalsohavesteady-state detonation velocities,but these velocities are more variable thanthoseofmolecular explosivesandareinflu-enced by such factors as diameter of thecharge, temperature, and confinement.HISTORICALDEVELOPMENTThe first known explosive materialwas blackpowder, a mixture of potassium nitrate(saltpeter), charcoal, and sulfur. As such it is acomposite explosive whose properties aredependent uponhowfinelydividedeachofthe ingredients is, and how intimately they aremixed. The exact origins of black powder arelost inantiquity. Publications referring toitseem about equally divided between those thatattributeitsorigintothird-orfourth-centuryChina"andthosethat placeit closertothe13th century, at about the time of RogerBacon's written description in 1242.9-13Nevertheless, its use did not become verypopular until the invention of the gun byBerthol SchwartzintheearlyBOOs; anditsfirst recorded use in miningdid not occur forover 300 years after that. First usedfor blast-ing in 1627, the productionand application ofblack powder played a critical role in the rapidexpansionof theUnited States intheearly19th century as canals were dug and railroadsbuilt to span the continent.Forover200years blackpowder wastheonly blasting agent known, but the 1800sbroughta number of rapiddevelopments thatledtoitsdemise, replacingitwithsaferandmore powerful explosives. Table 37.2 presentsa chronological summaryof some of thesig-nificant discoveriesofthe 1800s. Credit forthe first preparation of NG is generallyascribed to AscanioSobrero in Italy in1846.Swedish inventors Emmanuel Nobel and hisson Alfred took an interest in this powerfulliq-uid explosive and produced it commercially in1862. However, its transportation and its han-dling were very hazardous, and eventuallyAlfred Nobel discoveredthat NG absorbed intoagranular typeof material (kieselguhr)wasstillexplosive, but wasmuchsafer tohandleand use than the straight liquid. This newinvention, called"dynamite;' wasdifficult toignite by the usual methods used for pure NG.Therefore, also in1867, Alfred Nobel devisedthe blasting cap using mercury fulminate. Withthisdevelopment dynamitebecamethefoun-dation of the commercial explosives industry.For military and gun applications blackpowder continuedto be theonly explosive ofTABLE 37.2 Nineteenth CenturyExplosive Discoveries1800 Mercury fulminate1846 Nitrocellulose1846 Nitroglycerin1847 Hexanitromannite1862 Commercial production of nitroglycerin1867 Dynamite1867 Blasting cap1867 Ammonium nitrate explosive patented1875 Blasting gelatin and gelatin dynamite1884 Smokeless powder1886 Picric acid1891 TNT1894 PETN1748 KENTANDRIEGEL'SHANDBOOKOF INDUSTRIALCHEMISTRYANDBIOTECHNOLOGYchoice as a propellant or burstingcharge untilthe inventions of the late1800s, when smoke-lesspowder, basedonnitrocellulose, provedto be a cleaner, safer, and moreeffective pro-pellant thanblackpowder.The synthesis ofpicricacid(2,4,6-trinitrophenol) followedbyTNTandPETNgave solid, powerful, molec-ular explosives of more uniformperformancefor use in bombs and artillery shells.The main explosives used inWorldWar Iwere TNT, Tetryl (2,4,6-trinitrophenylmethyl-nitramine), and Hexyl (hexanitrodipheny-lamine), and in World War II they wereTNT, PETN, andRDX(l,3,5-trinitro-l,3,5-triazacyclohexane)."Inthe industrial arena the production ofblackpowder inthe United States droppedprecipitously after reaching a peak of277 millionlb in1917.iSBy the mid-l 960sithadceasedtobe of commercial significance,but during the same time period dynamiteproduction rose from 300 million Ib to600 millionlb.In 1947 a spectacular accident ofcatastrophic proportions usheredinthenextrevolutionin explosives. Fertilizer-grade AN,in the form of prills(small sphericalparticlescoatedwithparaffintoprevent caking), wasbeing loaded into ships in Galveston Bay,Texas. Alongwithother cargo, oneof theseships, the partially loaded SSGrandcamp,contained2300tonsof thismaterial. Onthemorningof April 16, soonafter loadingwasresumed aboardthe Grandcamp, afirewasdiscovered in one of the holds containing AN.Effortsto extinguishthe fire were unsuccess-ful, andanhour laterthebulkof thecoatedfertilizer detonated, killing 600 people andinjuring3000.16This tragedy, along with several other large-scale accidents involving AN explosions,finallyledresearchers totheconclusionthatinexpensive, readily available, fertilizer-gradeANcould be usedas the basis for modemindustrial explosives.Soonaftertheadvent of porousANprills,introduced in the early 1950s, investigatorsrealizedthat theseprillsreadily absorbed justthe right amount of Fa to produce an oxygen-balanced mixture that was both an inexpensiveand effective blasting agent, in addition tobeingsafe andsimple tomanufacture. Thistechnology was widely adopted and soon con-stituted 85 percent of the industrial explosivesproduced in the United States. I? With ANFO'scost and safety characteristics, it becamepractical for surface miners to drill largerboreholesandtoutilizebulk ANFOdeliverysystems.Nevertheless ANFO had two signifi-cantlimitations : ANis verywater soluble,sowet boreholes readilydeactivatedtheexplo-sive; andANFO's lowdensity of0.85 glcclimitedits bulk explosive strength. COOkl8hitupon theidea of dissolvingthe AN in a smallamount of hotwater, mixingin fuelssuchasaluminumpowder, sulfur, or charcoal, andaddingathickeningagent togelthemixtureandhold theslurriedingredientsin place. Asthis mixture cooled down, the AN salt crystalswould precipitate, but the gel would preservethe close contact between the oxidizer and thefuels, resulting in a detonable explosive .Otheroxidizersalsocouldbeadded,andthedensity could be adjusted with chemicalfoaming agents to vary the bulk explosivestrength of the product. With the addition of across-linkingagent , the slurry or water gelcould be converted toa semisolid materialhaving somewater resistance. Thelatestsig-nificant development inindustrial explosivesactuallywasinventedonlyafewyearsafterslurries.19abWater-in-oil emulsionexplosivesinvolveessentiallythesameingredients thatslurrycompositeexplosivesdo, butinadif-ferent physical form. Emulsion explosives arediscussed fully under the section titled"ExplosivesManufactureand Use."The main developmentsin military types ofexplosives since World War II have beentrends toward the use of plastic bonded explo-sives (PBXs) and the developmentof insensi-tive high explosives. Drivingthesetrendsaredesires for increased safety and improvedeconomics intheprocessof replacingagingTNT-basedmunitions andbombfills. PBXsinvolve the coating of fine particles of molec-ular explosives such as RDX and HMX(1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane)with polymericbindersand thenpressingtheresultant powder under vacuum to give a solidCHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1749masswiththedesireddensity. Thefinal formor shape usually is obtained bymachining.Explosives such as triaminotrinitrobenzene(TATB), nitroguanidine," and hexanitrostil-bene(HNS)21 areof interest becauseof theirhighlevels of shockinsensitivity and thermalstability. Thesynthesis of manynew,poten-tiallyexplosive compounds isa veryactiveand ongoingarea of research,22,23but recentlyinterestalso has focusedon composite explo-sives similar to those used by industry.Examples areEAK, a eutecticmixture of eth-ylenediamine dinitrate, AN, and potassiumnitrate," and nonaqueous hardened or castemulsion-based mixtures."CLASSIFICATIONOF EXPLOSIVESThe original classification of explosivesseparatedthemintotwoverygeneral types:low andhigh, referringtotherelativespeedsoftheir chemical reactions and the relativepressures producedbythese reactions. Thisclassificationstill is used but is oflimited util-ity because the only low explosives of any sig-nificance are black powder and smokelesspowder. All other commercial and militaryexplosivesare highexplosi ves.High explosives are classified further accord-ing to their sensitivity level or ease ofinitiation.Actuallysensitivityis moreofa continuumthan a series of discrete levels, but it is conven-ient to speak ofprimary, secondary, and tertiaryhigh explosives. Primary explosives are themostsensitive, beingreadilyinitiatedby heat,friction, impact, or spark. They are used only invery small quantities and usually in an initiatoras part of an explosive train involving less sen-sitive materials, such as in a blasting cap. Theyare very dangerous materials to handle andmust bemanufactured withtheutmost care,generally involvingonlyremotelycontrolledoperations. Mercury fulminate, used in Nobel'sfirst blastingcap, isin thiscategory,asis themore commonly usedlead azide. On the otherend of thespectrumare the tertiaryexplosivesthat aresoinsensitivethat theygenerallyarenot considered explosive.By far the largest grouping is secondaryexplosives, which includes all ofthe majormilitaryand industrial explosives. They aremuch lesseasilybrought todetonationthanprimary explosivesandarelesshazardous tomanufacture. Beyondthat, however,general-izations aredifficult becausetheir sensitivityto initiation covers a very wide range.Generally, the militaryproducts tend to bemore sensitive and the industrialproducts lesssensitive, but all are potentially hazardous andshould be handled and stored as prescribed bylaw. Table 37.3 lists someof the morepromi-nent explosives of each type, along with a fewof their properties.For industrial applications, secondaryexplosivesaresubdividedaccordingtotheirinitiation sensitivity into two classes:Class 1.1 andClass 1.5. Class 1.1explosivesare sensitive to initiationbyablastingcapand usuallyare used in relativelysmall-diam-eter applicationsof1-3-in. boreholes. Class1.5 (blasting agents) arehighexplosives thatare not initiatedbya Standard#8electricblastingcapunder test conditionsdefinedbythe U.S. Department of Transportation(DOT) , and that pass other defined testsdesigned toshowthat the explosive is "soinsensitive thatthereis verylittleprobabilityof accidental initiation toexplosionor of thetransitionfromdeflagrationtodetonation.v"Beingless sensitive,blasting agentsaregen-erally used in medium- and large-diameterboreholes and in bulk applications.Dynamitesare always Class 1.1, but other compositeexplosivesmade frommixturesof oxidizersand fuels can be made either Class1.1 or1.5,depending uponthe formulation and the den-sity. Densityplays a significant role intheperformanceof most explosives, andthis isespecially truefor slurry and emulsion explo-sives wherethedensity maybeadjustedbyair incorporation, foamingagents , or physicalbulking agents, irrespectiveof the formula-tion. Blastingagent (class 1.5) classificationisofinterest becauseregulations governingtransportation, use, and storage areless strin-gent for blasting agents than for Class 1.1explosives. (Propellants and fireworks areclassifiedby the DOTas Class 1.2or 1.3explosives, andblastingcapsanddetonatingcordasClass 1.4.)TABLE37.3SomePropertiesofCommonExplosives~ .....UIDetonationDetonationExplosive0MolecularDensityVelocityPressureEnergyj;jCommonNameSymbolCompositionWeight(glec)(Ian/sec)(kilobars)(cal/g)~PrimaryExplosives~ CMercuryfulminateHg(CNOh284.73.64.7220428~LeadazidePb(N3)z291.34.05.1250366mSilverazideAgN3149.95.16.8452C)mLeadstyphnateC6H(NOz)30ZPb468.32.54.8150368"-enMannitolhexanitrateMHNC6Hs(ONOz)6452.21.78.33001,420:::I:(Nitromannite)):loZDiazodinitrophenolDDNPC6HzN4OS210.11.56.6160820cTetrazeneCzHsNIQO188.21.5658D:l0SecondaryExplosives0 '"NitroglycerinNGC3Hs(ONOz)3227.11.67.62531,4800PentaerythritoltetranitratePETNCCCHzONOz)4316.21.67.93001,510."TrinitrotolueneTNTCH3C6HzCNOz)3227.01.66.9190900ZEthyleneglycoldinitrateEGDNCzHiONOz)z152.11.57.41,430c cCyclotrimethylenetrinitramineRDXC3H6N3(NOz)3222.11.68.03471,320en-I(HexogenorCyclonite)::aCyclotetramethylenetetranitramineHMXC4HsNiNOz)4296.21.99.13931,350s ....(Octogen)(")TrinitrophenyImethyInitramine(NOZ)3C6HzN(CH3)NOz287.21.47.6251950:::I:m(Tetryl)~NitroguanidineNQCH4N3NOz104.11.67.6256721en-INitromethaneNMCH3NOz61.01.16.21251,188::aNitrocelluloseNCVariable1.46.4210950< ):loTriaminotrinitrobenzeneTATBC6H6N3(NOz)3258.21.87.9315829ZDiaminotrinitrobenzeneDATBC6HsNz(NOz)3243.21.67.5259993cEthylenediaminedinitrateEDDNCzHIQN406186.11.56.8948D:l(5EthylenedinitramineEDNACZH6NzCNOz)z150.11.57.62661,080-Im(Haleite)(")PicricacidC6H3O(NOz)3229.11.77.42651,000:::I:ZAmmoniumpicrateC6H6NO(NZ)3246.11.66.98000 ....(ExplosiveD)0PicramideC6H4N(NOzh228.11.77.31,070C)200C), and highenergy properties make these crystalline com-pounds popular asprojectileandbombfillsand for use in cast boosters and flexible, sheetexplosives. HMX has superior detonationproperties anda higher melting point thanRDXbut it is more difficult and more expen-sivetomanufacture. Reaction I showstheformation of RDX by the action of nitric acidon HMT. Schematically, RDXformationcanbe pictured as nitration of the three "outside"nitrogenatoms of HMT(inmore accurate,three-dimensional representations all fournitrogens are equivalent) with removal of the"inside" nitrogen and methylene (-CH2- )groups. AN (NH4N03)and formaldehyde(CH20)are producedas by-products butcanbe used to form more RDX with the additionof aceticanhydride, asshown inReaction 2.In actual practicethese two reactions are runsimultaneously, as shown in the combinedreaction to produce approximately two molesof RDX for each mole of HMT.HMX was discovered as an impurityproducedinthe RDXreaction. It is com-posed of an eight-membered ring rather thanthe six-memberedringof RDX. The latteris more readily formed than the eight-membered ring, but with adjustment of reac-tion conditions (lower temperature anddifferent ingredient ratios), HMX formationcanbefavored. Schematicallyitsformationcan be pictured by nitration of all four nitro-gens in hexamethylene tetramine andremoval oftwomethylene groups as indi-cated inReaction 3. Toobtain pure HMXthe RDX"impurity" must be removed byalkaline hydrolysis or bydifferential solu-bilityin acetone.HNS12,2',4,4',6,6' -Hexanitrostilbene)This is a relatively new explosive having beenpreparedunequivocallyfor thefirst timeinthe early1960s.30a,b It is of interest primarily1754 KENTANDRIEGEL'S HANDBOOKOF INDUSTRIALCHEMISTRYANDBIOTECHNOLOGYReaction1HMTReaction2Formaldehyde AN AceticanhydrideCombined ReactionRDX AceticacidReaction3for two reasons: (1) its high melting point(316C) and excellent thermal stability, and(2)itsuniquecrystal-habit-modifyingeffectsoncast TNT.Theformermakes HNSusefulin certain military and space applicationsas well as inhot, very deep wells, and thesecond property is used toimprove TNTcast-ings. It can be manufactured continuouslyby oxidative coupling of TNT as shownbelow.Thisrelativelysimpleprocessfromreadilyavailable TNT and household bleach (5%NaOelsolution) has been showntoinvolveaseriesof intermediatestepsthat giveHNSinonly lowtomoderateyields (30-45%) withmanyby-products. Althoughit also involvesthe use of expensive organic solvents thatmustbe recovered, thissynthesis is usedcom-mercially.31,32Studiestoimprovethisprocessconstitute an activeareaof research.NaOCI-----+CH,OHTHFo-is-cTNT HNSCHEMICALEXPLOSIVES ANDROCKET PROPELLANTS 1755TATB(1,3,5-Triamino-2,4,6-trinitrobenzenelThis highlysymmetrical explosivemoleculehas evenhigher thermal stabilitythanHNS(greater than 400C) and has become ofspecial interest in the last two decadesbecause of its extreme insensitivity.Pv' ?"Because its accidental initiation is highlyunlikely, TATBhas been usedin nuclearwar-heads and is being exploredin plasticbondedsystems for anumber of military andspaceapplications.i" Currentlyit is manufactured inlarge-scale batch processes that are littlechangedfromitsoriginal synthesisover 100years ago. The two-step processinvolves trini-tration of trichlorobenzene followed byaminationtodisplacethechlorinegroups asshown below.

clMclNaNO,H2SO.(SO,)----+150'C4hrproduct or to change its particle size byrecrystallization. Alsothestartingmaterial isexpensive and not very readily available.More recently a similarsyntheticprocedurestarting with 3,5-dichloranisole was reported."DDNP(2-Diazo-4,6-dinitrophenollThis yellow-to-brown crystalline material(meltingpoint 188C) is a primar y explosiveused as the initiator charge in electric blastingcapsasanalternativetoleadazide. It is lessstablethanleadazidebut muchmorestablethanleadstyphnate, andisastronger explo-sivethaneither of thembecause itdoesnotcontainany metal atoms. DDNPis also char-acterized as not being subject to dead pressing(testedat pressures as highas 130,000 psi).It wasthe first diazocompounddiscovered(1858) and was commercially prepared in1928, It is manufactured in a single-step,batch process by diazotizing a slurry ofsodiumpicramatein water.TrichlorobenzeneTrinitrotrichlorobenzeneThe structure shown is convenient forvisualization purposes, but DDNP actuallyexistsinseveral tautomeric formswithform(2) apparentlypredominating.0-02NyYN=NYN02DDNPNaND,-- HCISodiumPicramateCI NH2

C1 yCIH2NYNH2N02N02TATBBoth steps require high temperature andconsiderable reaction time but give 80-90percent yields. Themajor problemareasarechloride impurities inthe final product andtheexcessivelyfineparticle sizeof thefinalproduct. Because TATB is highly insolubleinmost solvents, it isdifficult topurifythe0-O'N'rN=NN02(I )o,NhN",NyN02(2)1756 KENTANDRIEGEL'SHANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYCH20HIHOH2C-C-CH20H+HCa(OOCHhJtHOH CalciumFormate2PentaerythritolNG(NitroglycerinorGlyercol TrinitratelThisnitrateester isoneof onlyaveryfewliquid molecular explosives that are manufac-turedcommercially. It isaclear, oilyliquidthat freezes when pure atl30C. As seen in thehistorical section, the first practical use ofNGwas in dynamites, where it is still used todaymore than100 years later. It also is used as acomponent inmultibasedpropellants andasa medicine to treat certaincoronaryailments.This latter usage is attributed to NG'sability to be rapidly absorbed by skin contactor inhalation into the blood, where it acts as avasodilator.(Athighexposurelevels suchasindynamite manufacture andhandling, thispropertyis responsible for the infamous pow-der headache.) NGisundoubtedlythemostsensitive explosive manufacturedin relativelysolidalcohol addedslowlywithmixingandcooling. PETNisnot very solubleinnitricacidor water andisreadilyfiltereddirectlyfrom the acid or after dilution of the acid withwater. Water washing and recrystallizationfrom acetone-water mixtures give the desiredparticle size ranges and the desired purity.PETN can be made either batchwise orcontinuously for large-scale production.Pure PETN is a white, crystallinesolid withameltingpoint of 141.3C. Because ofitssymmetryit issaidtohavehigher chemicalstability than all other nitrate esters."Relatively insensitive to friction or sparkinitiation, PETN is easily initiated by anexplosive shock and has been describedoverall as one ofthe most sensitive, non-initiating, military explosives." As with mostexplosives, thedetonationvelocityof PETNvaries with the bulkdensityof the explosive.Most military applications of PETNhavebeen converted to RDX because of its greaterthermal stability. However, in industryPETNis widely used as the major component in castboostersforinitiatingblastingagents, astheexplosive corein detonatingcord, andas thebase load in detonators and blasting caps. Forsafetyin handling, PETNisshippedin clothbags immersed in water-alcohol mixtures anddried justbefore use.Ca(OH),~Ca(OH),~Formaldehyde AcetaldehydeThesodiumpicramate startingmaterial isitself explosive, but is commerciallyavailableas a chemical intermediate. It can be made bythe reduction of picric acid with reducingagents such as sodiumsulfide. The keytomaking usefulDDNP is to control the rate ofdiazotizationso that relatively large, roundedcrystals are formed instead of needles orplatelets that do not flow or pack well.ForPETNmanufacturethepentaerythritolstarting material can be readily purchased as acommodity chemical fromcommercial sup-pliers. The nitration is relatively simple,involvingonlynitricacid(96-98%) andthePETN(Pentaerythritol TetranitratelAlthoughknownasan explosivesince1894,PETN was used very little until afterWorldWar I whenthe ingredients tomakethe starting material became commerciallyavailable. The symmetrical, solid alcoholstarting material, pentaerythritol, is madefromacetaldehydeandformaldehyde, whichreact by aldol condensation under basiccatalysis followedbya crossed Cannizzarodisproportionation to produce the alcohol andformate salt. Although the reaction takes placein a singlemixture, it isshown below in twosteps for clarity.CHEMICALEXPLOSIVES ANDROCKET PROPELLANTS 1757TABLE37.4 General Types of Dynamite large quantities. Its sensitivity to initiation byshock, friction, andimpact isveryclosetothat of primary explosives, and extreme safetyprecautions are taken during manufacture.Pure glycerin is nitratedin veryconcentratednitricandsulfuricacidmixtures (typicallya40/60 ratio), separatedfromexcessacid, andwashedwithwater, sodiumcarbonate solu-tion, and water again until free from traces ofacidor base. PureNGisstablebelow50C,but storageisnot recommended. It istrans-portedover short distancesonly asanemul-sion in water or dissolved in an organicsolvent suchasacetone. Traditionallyit hasbeen made in large batch processes, but safetyimprovementshaveledtotheuseofseveraltypes ofcontinuous nitrators that minimizethe reaction times and quantities of explosivesinvolved. Because of its sensitivity, NG is uti-lizedonlywhendesensitizedwithother liq-uidsor absorbentsolidsor compoundedwithnitrocellulose.1.Straightdynamite2. Ammoniadynamite("extra" dynamite)3. Straightgelatindynamite4. Ammoniagelatindynamite("extra"gelatin)5. Semigelatin dynamite6. PermissibledynamiteGranular texturewith NGas the majorsource ofenergy.AN replacingpart of theNGandsodiumnitrateof the straightdynamite.Small amountofnitrocellulose added toproducesoft to toughrubberygel.AN replacingpart ofthe NGand sodiumnitrate of the straightgelatin.Combination of types2 and4 within-betweenproperties.Ammoniadynamiteorgelatinwithadded flameretardant.DynamiteDynamite is not a single molecular compoundbut amixtureof explosiveandnonexplosivematerials formulated incylindrical paper orcardboard cartridges for a number of differentblastingapplications. OriginallyNobel sim-ply absorbed NGinto kieselguhr, an inertdiatomaceous material, but laterhereplacedthat with active ingredients-finelydividedfuels and oxidizers called dopes. Thus, energyis derived not only from the NG, but also fromthe reaction of oxidizers such as sodiumnitrate with the combustibles.The manufacture of dynamite involves mix-ing carefully weighed proportionsof NGandvariousdopestothedesiredconsistencyandthenloadingpreformedpaper shellsthroughautomatic equipment. Because dynamitesrepresent the most sensitive commercial prod-uctsproducedtoday, stringent safetyprecau-tions such as the use of nonsparking andvery-little-metal equipment, good housekeep-ing practices, limited personnel exposure, andbarricaded separations between processingstationsare necessary. Today, the"NG"usedindynamiteisactuallyamixture of EGDNand NG(formed by nitrating mixtures ofthe two alcohols),in which NGis usually theminor component. Table 37.4 lists thecommon general types of dynamites withtheir distinguishing features. The straightdynamites and gelatins largely have beenreplaced by the ammonia dynamites andammonia gelatins for better economy andsafety characteristics.PackagedExplosivesTheuseof NG-baseddynamitecontinuedtodecline during the 1990's throughout theworld. For example, by1995 therewasonlyone dynamite manufacturing plant left inNorth America, and in 2000 the dynamiteproductionat thisplant haddroppedtolessthanhalf theamount producedin1990. Thereasonsfor the declininguse of dynamiteareits unpopularpropertiesof sensitivity to acci-dental initiation and the headache-causingfumes. Both bulk and packaged emulsionshavebeen slowlyreplacing dynamite sinceabout 1980.Packaged emulsions are basically made withthe same manufacturing equipment as thebulk emulsions (seenext section). The fuel1758 KENTANDRIEGEL'S HANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYFig. 37.4. Commercial packaged emulsioncartridges.component usuallycontainswaxes andotherthickeners to give the emulsions a thick, putty-like consistency, and the oxidizer solutionoften contains both AN and a second oxidizersalt to produce optimumafter-blast fumes.After manufacture, the thick emulsion isextrudedinto packagingmaterial,normallyaplasticfilm. Thefinal productis thenclippedtogether with metal clips forming firm,sausage-like chubs. Some packaged emulsionsare also available in paper cartridges, designedtosimulatedynamitepackaging. Figure3704showssomecommercial packagedemulsioncartridges in both plastic and paper wrappings.To obtain reliable detonability in smalldiameters, the density of packaged emulsionsmust bemaintainedata relatively low value,typically 1.10-1.20 glee. Ontheother hand,somedynamites areavailablewithdensitiesinexcessoflAOglee. Thesehigher densityand energy dynamites have been the mostdifficult to replace with emulsions and arethe primary dynamite products currently inproduction.CHEMICALEXPLOSIVESANDROCKET PROPELLANTS 175917..--~l//Vpvc7U 4500Ql.!!!..~ 4000"0o~350050003000o 50 100 150 200 250 300Diameter (rrm)Fig. 37.5. Detonation velocity of ANFO versusdiameter andconfinement.efficientdetonabilityof ANFO. TheANprillparticle density and inherentvoid-space valuealsobecome important whenpredictingandcalculating the densities ofANFO blends withwater-geland emulsion explosives.The bulk density ofANFOranges from 0.80to 0.87 glcc. So, clearly about half ofthe ANFOis air or void space. All explosives require a cer-tain amount of entrained void space in order todetonate properly.These void spaces also playamajor rolein the detonationreaction by creat-ing "hot spots"under adiabatic compression inthe detonation front." The amount of voidspacein any given explosive and theresultantchangein densityhave a significant impact onthe detonation properties like detonation veloc-ity, sensitivity, and even energy release.Generallyspeaking, the detonationvelocityof an explosive will increase with densityuntil afailure point is reached. This failurepoint iscommonlyreferredtoasthecriticaldensityof that particular explosive. Theden-sity at thatpointis so high and the void spaceso low that the detonation cannotbe sustainedandfailureoccurs.Otherimportant parametersthat affect thedetonation velocity and performance ofANFOarechargediameter andconfinement.The detonation velocity of ANFO willincrease byabout 300 mls whenthe chargeconfinement is changed from a PVC tube to aSchedule 40 steel pipe. Asummaryoftestdata onANFOvelocity versus confinementand diameter is shown in Fig. 37.5.AmmoniumNitrateand ANFOANcontinues to be the most widely usedcomponent ofcommercial explosives. It isusedinnearlyall of thepackagedandbulkexplosivesonthemarket.Themanufacturingprocessis described in Chapter 29.Ammonia is basically the main raw materialneededtomanufacture AN. Someof the ANmanufacturersmaketheir ownammoniaandsome purchase it onthe open market. It isobvious that the cost ofmanufacturingANwill depend on the price ofammonia and,even more basically, natural gasfrom which itismade. Thevolatilityof ammoniaprices isshown by thefact thatin1992 it cost$95 perton and in1995 thecost was$207 per ton."Therearemanyproducersof ANinNorthAmericamakingboth ANsolution and explo-sive grade ANprills. The ANsolutionis usedin the manufacture of packaged and bulk emul-sionandwatergel explosives,andexplosive-grade ANprills are used to make ANFO.ANFO, the acronymfor amixture of ANandFO is the single most commonly used chemicalexplosive. (ANFOis an example of a compos-ite explosive as describedin an earlier section"Chemistryof CombustionandExplosions".)These low density AN prills are made by a spe-cializedprocess, inwhich internal voids arecreatedmakingtheprills porousandabletoabsorb the required 5.5-6 percentFO.ANFOalonerepresentsabout threefourthsof thecurrent volumeof commercial explo-sivesin usetodayaroundtheworld. Becauseof this, ANFOiscommonlyusedasarefer-encewhendefiningandcomparingexplosiveproperties. Some of theseimportant explosiveproperties include density, detonation velocity,and energy release.The crystal density ofAN is about1.72 glcc,and the particle density of explosive-gradeAN prills ranges from lAOto 1045 gleedependingupon the manufacturingprocess.Thisdifferencein crystal and particle densityrevealsthevolumeof poresorvoidscreatedby the specialized prilling process . The poros-ity of AN prillsis thepropertydesiredin themanufactureof ANFO, sincethisdetermineshow muchFO can be absorbed. Thisintimatemixture ofANwith FOis critical in the1760 KENTANDRIEGEL'SHANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYThebasicchemical reactionof ANFOcanbe describedwith the following equation:3NH4N03 + CHz~ COz + 7HzO+ 3Nz+ 880 cal/gUsing CHzto represent FO is generallyaccepted, but it really is an oversimplification,since it is a mixture of hydrocarbons. The heatenergyreleaseof 880 cal/gisthetheoreticalmaximum value based upon the heats offormation of the reactants and products.Of course, all of theproducts of detonationare gases at the detonation temperature ofabout 2700oK.The theoretical work energy that is releasedfromanexplosivereactioncanbecalculatedusing a variety of equations of state and com-puter programs."Explosiveenergycanalsobe measured by a variety of techniquesincluding underwater detonation of limitedsize charges with concurrent measurementsof the shock and bubble energies." Eachexplosivemanufacturerhasanenergymeas-urement andequationof statethat isusedtocalculateandreport theirproduct properties.This often leads to confusionand controversywhen explosive consumers try to compareproduct lines when given only technicalinfor-mationsheets. Sincetheoretical calculationsmust of necessity bebasedonanumber ofassumptions, theonlyvalidcomparisonsaredone in the field with product testing anddetailedevaluation of results.BulkEmulsionsDuring the past decade the commercial use ofbulk emulsion explosives continued toincrease. Bulk emulsion products began tosignificantly replace packaged products inunderground mining and in quarry opera-tions. Also, bulkemulsionand ANFOblendsbecame very popular in large volume open-pitmining operations. Emulsions are made bycombining an oxidizer solution and a fuelsolution usingahigh-shear mixingprocess.Theoxidizersolutionis normally90-95per-cent byweight of the emulsion. It containsAN,water,andsometimes asecondoxidizersalt, that is, sodiumor calciumnitrate. Thesolution must be kept quite hot, since thewateris minimized for increased energy, andthe crystallization temperature is typically50-70C. The fuel solution contains liquidorganic fuels, such as FO and/or mineraloils,and one or moreemulsifiers. An emulsifier isasurfaceactivechemical that has bothpolarand nonpolar ends ofthe molecule. In thehigh-shear manufacturing process, the oxi-dizer solution is broken up into smalldroplets, each of whichis coatedwith a layerof fuel solution. The droplets in thismetastable water-in-oil emulsion are basicallyheldtogether withtheemulsifier molecules,which migrateto the surfaceof the disperseddroplets. In today's explosives industry, muchof the research work is directed towardsdevelopingbetter andmoreefficient emulsi-fiermolecules that will improvethestoragelifeandhandlingcharacteristicsof thebulkand packagedemulsions. The emulsifiers cur-rentlyusedincommercial explosives rangefromrelativelysimplefattyacidesters withmolecular weights of300--400tothe morecomplex polymeric emulsifiers having molec-ular weights in excess of 2000.Figure 37.6shows a photomicrograph of anemulsion explosive at 400 power with the typi-cal distribution ofthe fuel-coated oxidizer solu-tiondroplets(normally1-5 urnindiameter).Figure37.7 showsabulkemulsionexitingaloading hose and displaying the soft ice cream-like texture typical ofbulk emulsions. Theviscositiesof bulkemulsionscanrangefromnearlyasthinas90 weight oiltoasthickasmayonnaise, dependingupontheapplicationrequirements. Emulsion viscosity increaseswith product cooling, but most emulsionscontinue to remain stable at temperaturesbelowOC, whichisconsiderablybelowthecrystallization temperature of the oxidizersolution. The oxidizer solution dropletsin theemulsion aretherefore held ina supersatu-ratedstate. Over time, thesurfacelayers cre-ated by the emulsifier molecules can bebroken,and the oxidizersolutiondropletsarefreetoformcrystals. Atthispoint theemul-sion begins to "break down" and lose some ofthe desirable properties. For this reason theFig.37.6. Photomicrographofa bulkemulsion.Fig. 37.7. Bulk emulsionexitinga loadinghose.1762 KENTANDRIEGEL'SHANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYemulsioncompositionmust beoptimizedfora particular applicationin terms of its productstability and usable storagelife.The intimatemixing of oxidizer and fuelinemulsions give theseexplosivesmuchhigherdetonation velocities when compared toANFO. For example, in 150 mmdiameterPVC ANFO has a velocity of about4000 m/sec, andasensitizedemulsionwouldhave a velocity closer to 6000 m/sec at aden-sityof1.20-1.25glcc. Also, thelayer of oilsurrounding each oxidizer solution droplet pro-tects the emulsion from extraneous water intru-sion and subsequent deterioration of theexplosive. Many studies have shown that whenmining operations use emulsion explosivesrather than ANFO, which has basically nowater resistance, the amount of nitrate salts inmine ground water is reduced considerably.Thiscan bea veryimportantfactor in today'senvironmentally consciousminingandexplo-sives industry.Bulk emulsionsare generallynondetonableperse andmust be sensitizedwithsome typeof densitycontrol mediumtobecomeusableblastingagents. That is, voids, creating"hotspots,"arerequiredtosustainthedetonationfront.Thetwomost commonlyuseddensitycontrol methods are hollow solid micros-pheres or gas bubbles created byanin-situchemical reaction. Both glass and plastichol-low microspheresarecommercially availableand used byexplosives manufacturers. Thein-situ chemical gassing techniques requireconsiderably more expertise and generallyutilize proprietary technology.In the past decade the use of sensitized bulkemulsions has increased considerably in under-groundmining. Much of this has beenduetothedevelopment of innovative loadingequip-ment andtechniques. Oneexampleof thisisshown in Fig. 37.8 which shows a small-volumepressure vessel that canbeusedfordevelopment andtunnelroundsutilizinghor-izontally drilled boreholes. The bulk emulsionblastingagentis pressurized inside the vesseland literally squeezed through the loadinghose into the boreholes . A continuouscolumnof explosivesis assuredby insertingthe load-ing hose to the back of the hole and extractingit as theproduct is loaded. Muchmorecom-plexundergroundloadingunitsareavailablefor loading bulk emulsion into boreholesdrilled at anyangle tothe horizontal fromstraight upto straight down. The emulsionexplosives usedinthesespecializedloadingunits were specifically designed for under-grounduseovertwentyyearsago, andhavebeensuccessfullyusedinundergroundmin-ing operationsaround the world. The fuel andoxidizercontents arecarefullybalanced, andthis, combined with the excellent water resist-anceanddetonationefficiency, resultsinthenear elimination ofafter-blast toxic fumes,such as CO, NO, and N02. The fume charac-teristics of this product have been shown to beconsiderably superior toeither dynamite orANFO. Forexample, aseriesof tests inanunderground chamber inSwedencomparedthe after-blast fumes of this emulsion toANFO. TheCOwas reducedfromII tolessthan 6 Llkgofexplosive, andthe NOplusN02wasreduced fromabout 7toless than1 Llkg of explosive.fMany open-pit quarries also use bulkemulsions for their blasting operations. As thesizeof thequarry increases, thesizeof theexplosiveloadingtrucks alsomust increase.Truck payloads can range from 5000 to30,0001bof product. Figure 37.9shows anemulsionpumper truckinaquarry insouthFlorida. Theseparticulartrucks, withapay-load of about 20,000 lb, are speciallydesigned for a site-mixed system, inwhicheach truck is an emulsion manufacturing unit.Combining nonexplosive raw materialsdirectly onthe truck maximizes safetyandminimizesrequirement for explosivestorage.This particular bulk emulsion is manufac-turedat aratebetween300and500 Ib/minandsensitizedtothedesireddensitywithachemical gassingsystemasit isloadedintotheboreholes. Figure37.10showsaFloridablast inprogress. Notetheejectionof card-board tubes fromsome holes. These tubesmustbe usedin mostareastokeep thebore-holes fromcollapsing in the layered, corallimestoneformation.Manyof thelargevolumemetal andcoalmining operations around the world have bothCHEMICALEXPLOSIVES ANDROCKET PROPELLANTS 1763Fig. 37.8. Undergroundpressurevessel loaderfor bulkemulsion. (Courtesy DynoNobel)bulkemulsionand AN prillsstoredeitheronsite or nearby so that any combination ofthese two productscan be used.Figure 37.11showsatypical explosivestagingarea inalarge open-pit coal mine inWyoming. Theexplosivetruck inthe foregroundhas com-partments onboardforemulsion, ANprills,and FO, so any combination of products rang-ingfromstraightemulsiontostraight ANFOcanbe loaded. Thetruckhas acapacityofabout 50,000 lb and can deliver product to theboreholes at upto aton per minute. Eachborehole cancontainas muchas 5tons ofexplosive, and some of the blast patternscancontain as much as10 million total pounds.The emulsion!ANFO explosive blend selec-tionto beusedin anygiven miningapplica-tion depends upon many factors. Typically,ANFOistheleast expensiveproduct, but italso has the lowest density and no waterresistance.Asemulsionisaddedto ANFOitbegins to fit into the interstitial voids betweenthe solid particles and coat the ANprillsincreasing the density, detonation velocity,andwater resistance. The density increasesnearly linearlywith percent emulsion fromabout 0.85 glccwith ANFO to about 1.32 g/ccwitha50/50 blend.Thisrangeofemulsion!ANFOblends is commonly referred to asHeavyANFO. Asthedensityincreases, theamount ofexplosivethat canbeloadedintoeach borehole increases, and either drillpatternsbased on ANFO can be spread out orbetter blasting results can be obtained.1764 KENTANDRIEGEL'S HANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYFig. 37.9. Bulk emulsionloading truckina Floridaquarry.It iscommonlyaccepted intheexplosiveandminingindustrythat at least40-50per-cent emulsion is required to protect theHeavy ANFO blend fromborehole waterintrusion. Pumped explosive blends with60-80 percent emulsion can even be usedwhen severe water conditions are encoun-tered. Theseproduct s can be pumpedthroughaloadinghose, whichcanbelowered tothebottom of the borehole and displace the waterduringloading. Truckssimilar tothat showninFig. 37.9canbeusedfor theseproducts .Most Heavy ANFO productsare more simplymixedandloadedthroughanauger intothetopof boreholes. For Heavy ANFOproductsthe holes must be either dry or dewateredusmgpumps .The basic chemical composition of a typicalall-AN oxidizer emulsion explosive wouldbe: AN plus about 15 percent water plus about5 percent fuels. The fuels may contain fuel oil,mineral oils, and emulsifiers,themajorityofwhich can generally be described as CH2hydrocarbonchains. Therefore, a very simpli-fied chemical reactionfor a basic emulsionissimilar to thatfor ANFOshown above.Byadding 15percent water totheANFOreactiondescribedearlier, the theoret ical heatenergy release is reduced from 880 to680 callg. ThedifferenceistheenergypriceCHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1765Fig.37.10. Floridaquarryblast inprogress.paid for using water and converting it to steamin the detonation reaction. The advantages anddisadvantages of usingANFOor emulsionsbegin to becomeclear. ANFO is easily mixedandisprobablytheleast expensiveformofexplosiveenergy,but it hasnowaterresist-ance and has a relatively low loading density.Emulsions are considerably more compli-cated to formulate and manufacture, butthey have excellent water resistanceand moreflexibility in terms of density, velocity,andenergytomatchrocktypesandblastingapplications.INITIATIONSYSTEMSThe first reliable initiation system forcommercial explosives could probably betraced back to Alfred Nobel'sinvention of theblasting cap in 1864. This, combined withhis subsequent inventionof dynamite aboutthree years later, basicallystarted the moderneraofblasting. In thecenturythat followed,the initiation systems became more andmoresophisticatedandsafe. Shortandlong-period delay electric blasting caps wereperfected and detonating cord was developed.Detonating cord is a flexible cord made of clothor plastic with acore load of high explosives,usuallyPETN. Stringsorcircuits of detonat-ing cord could be used to initiate severalexplosive charges with only one blasting cap.Prior to about1950 most of the commercialexplosives in the market were reliably deton-able withjust a blasting cap or detonatingcord as the initiator. Then came the advent ofANFO and later water-gels, invented byMelvin A. Cook in 1957. These explosiveproducts were considerably less sensitive thandynamites and required larger "booster"charges for reliable detonation. At first, a highdensityand highvelocitydynamitewas usedas thebooster charge, andlater TNT-basedcast boosters came into the market. These castboosters continuetobeusedtodayinnearlyall large mining operations. Cast TNT byitself is not reliably detonablewith a blastingcap or detonatingcord, and so 40-60 percent1766 KENTANDRIEGEL'S HANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYFig. 37.11. Typical bulkexplosivesstagingarea in a largeopen-pitmine.PETN is normally added to the TNT melt andsubsequent cast. The combination ofTNT andPETNis calledPentolite. TNThas a meltingpoint of about 80C, which makes it an excel-lent base explosive for casting into forms. Themilitaryhas used this concept for decadesforfilling bomb casings. Once the TNT hasmelted, other material can be added togive thefinal cast explosivecompositionthedesired properties. In the case of Pentolitecast boosters the added material is finelydivided PETN. Commercialcast boostersareavailable in a variety of sizes fromabout10-800 g as shown in Fig. 37.12.Thisvery brief historyrelatesthedevelop-ment inthecommercial explosivesindustryof an explosive loadingandinitiationsystemthat emphasizedsafety. Anentirepatternofboreholes can now be loaded with an insensi-tive blastingagentprimedwithcastboostersCHEMICALEXPLOSIVES ANDROCKET PROPELLANTS 1767Fig. 37.12. Somecommercial cast boosters.on detonating cord down lines. The downlines can then later be tied to surfacedetonat-ing cord line, andthe entire blast initiatedwith just oneblastingcapaftertheblastpat-ternhasbeencompletelyclearedof person-nel.Delayelementswerealso developedthatcouldbeplacedbetweenholestocontrol theborehole firingsequenceformaximumblastmovementand rockfragmentation.Non-ElectricInitiationIn 1967 Per-Anders Persson of Nitro Nobel ABinSweden (now part of DynoNobel Europe)invented a non-electric initiation system,designated Nonel" that has revolutionized thisaspect of theexplosivesIndustry. TheNonelsystemconsistsof anextrudedhollow plastictube that contains an internal coating of a mix-ture of powdered molecular explosive and alu-minum. Theplastictubeisinsertedintoandattachedtoaspeciallydesigneddetonator orblasting cap. The Nonel tubing can be initiatedbya numberof starterdevices, one of whichuses a shotgun shell primer. The explosive/alu-minummixtureexplodesdowntheinsideofthe tubeat about 2000 rn/sec and initiates theblasting cap. The tubing is about 3 mm outsidediameter and1 mminsidediameter, andtheexplosive core load is only about 18 mg/m, noteven enough to rupturethe tubing. The Nonelproduct is not susceptible to the hazard associ-atedwithelectricblastingcapswhereinpre-mature initiation by extraneous electricsources canoccur. Figure 37.13is aphoto-graph of both an electric blasting cap with thetwoelectrical wiresandatypical Nonel unitwith the plastic tubing.The 1990ssawalargeincreaseintheuseof Nonel products around the world toreplacebothelectricblastingcapsanddeto-nating cord down lines. It has long beenknownthat detonatingcorddownlines dis-rupt andpartiallyreact withblastingagentscausingsome degree ofenergy loss. Also,the use of surface detonating cordsto initiate1768 KENTAND RIEGEL'SHANDBOOKOF INDUSTRIAL CHEMISTRY ANDBIOTECHNOLOGYFig. 37.13. Anelectricblasting cap showingelectrical wires, typical Nonel unit withplastictubing.blasts can lead to noise complaints. As aresult , long-leadNonels weredevelopedtoreplace thedetonatingcordin boreholes. Asdelayelements wereperfectedfor theNonelblastingcaps, their application andusegrewevenfurther andespeciallyinundergroundminingwherealargepercentage of blastingcapsis used.Detonator manufacturersare now perfectinginitiation systems using electronic blastingcaps containing programmable delay circuitryandremoteinitiationfeatures. Themanufac-turing cost ofthese units is currently rela-tively high, but as the science progresses theseelectronicdetonatorswill likely be a wave ofthe future.PART II. ROCKETPROPELLANTSA rocket is a device that uses the expulsion ofinternally generated gases as a source ofmotivepower. Thegasesusedforpropellingthe rocketare generatedby chemicalreactionof afuelandanoxidizer. Theforcethat actsagainst a rocket as gases are expelled is calledthrust. Becauserockets carrytheir ownfueland oxidizer and do not rely on air, the thrustfromreaction(combustion) of thepropellantchemicals will act in a vacuum. Thus, rockets,unlikeinternalcombustion engines,are capa-ble of providingpowerin spaceaswell as inthe earth'satmosphere.The use of rockets has been traced to13thcenturyChina, but it wasnot until thedevelopment of the liquid-fueled V-2 inGermany during World War II that a practicallong-range missile using rocket propulsionwas achieved. Workduring the early 20thcentury by such pioneers as KonstantinTsiolkovsky in Russia, Robert Goddard inthe United States, and Hermann Oberth inGermany provided the basis for thesuccessful German effortand the spectacularspaceexplorationstudies that followed. Thelaunchingintoorbit of theSputniksatellitefrom the Soviet Union in1957 was theinitialCHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1769CaseNozzle~yExpansionThroat ConeFig. 37.14. Schematicdrawingof a simplerocket.ExitPlaneevent in a huge expansionof rocket develop-ment effortsinrecent years. Thesedevelop-ments have resultedin rockets used for threeprincipalapplications: space exploration and satellite launching strategic missiles tactical missilesSpace exploration efforts have been verywell publicized in recentyears. These effortshave includedsuch notable developments, inaddition to Sputnik, as the launching ofmanned rockets (with the first astronautsYuriGagarinintheSovietUnionandAlanShepard in the United Sates), the Apollomissionsto the moon (with Neil Armstrong'smomentous first step), the Russian,American, andInternational spacestations,the U.S. space shuttle program, and theexploration of the solar system by suchspacecraft as the Russian Venera and theU.S. Pioneer, Mariner, and Voyager. Perhapsless well publicized, but of greatcommercialand strategic importance, has been thelaunchingof satellitesfor purposes of com-munication, mapping, and surveillance.Launchvehicles for theU.S. spaceprogramhaveincludedthe AtlasAgena, Delta, Juno,Saturn, Scout, Thor, and Titan rockets.Thespaceexplorationefforts wereparal-leled in the United States and the SovietUnion bythe development ofrocket-pow-ered missilesfor strategicmilitaryuse. SuchU.S. systems as theAir ForceMinuteman,Peacekeeper,and Small ICBM and the Navysubmarine-launchedPolarisandTrident arewidelydeployed.The use ofmissiles for tactical militaryapplicationshasalsobeenanareaof majordevelopment since World War II. Among thefirst such applications were the JATO(rocket assistedtakeoff) units usedtopro-videpowertoboost launchingof airplanes.Tactical missiles have becomeanimportantcomponent of weaponry and include U.S.rockets such as the Navy Sidewinder andStandard Missile, the Army Hawk andHellfire, and the Air Force Sparrow,AMRAAM, andPhoenix.PRINCIPLESOFROCKETPROPULSIONTheflight of rockets isbasedonthethrustachieved by expellinggases from the aft endof the missile;thisprovidesa forwardimpe-tus. Aschematicdiagramof a simplerocketis showninFig. 37.14. Combustionof the1770 KENTANDRIEGEL'S HANDBOOKOF INDUSTRIALCHEMISTRYANDBIOTECHNOLOGYpropellant causes pressurization of the cham-ber by hot gases; the pressure from the gasesis counterbalanced by the strength of thechamber. At a narrowopening, the throat,gasesare allowed to escape, providing thrust.If therewerenoexpansioncones, andgaseswere expelled at thethroat, theforce, F,act-ing to propel the rocket would be:F = AtPcwhere At is the area of the throat and P, is thechamber pressure. When an expansion cone ispresent, anewtermcalledthethrust coeffi-cient, Cr,entersthe equation:F =AtPcCrThevalueof Cr depends ontheratioof thechamberpressuretothepressureat theexitplane, andontheratioof thethroat areatothe exit plane area. The optimumperform-ance of a rocket resultswhenthepressureattheexit plane, Pe, is equal tothepressureofthe surrounding atmosphere (which is oneatmospherefor firingsat sealevel andzeroatmospheres in space).Because thrust is dependent on motordesignand the rate of propellant combustion,it isnot aconvenient measureof propellanteffectiveness. Aparameter that is used tocompareeffectivenessis the specific impulse,Jsp, which is equivalent to the force divided bythe mass flow rate of the propellant:J s p = ~ = Jrwhere wis the weight flowrate of thepropellant, Wis the total weight of the propel-lant, andt is the time. Because theimpulseisdependent on a variety ofparameters, it is cus-tomarytousethestandardspecificimpulse,J:,ps'which is the value of the specific impulsefor anideal rocket motor firedat 1000 psi,exhaustingto14.7 psi, withno heatloss,andwithanozzle of 15half-angle. Frequently,measured or delivered impulse, Jspdvaluesfrom motor firings will be converted to J:,ps forcomparison with previous firings and withexpectations. The ratio ofdelivered to pre-dicted impulse is termed the efficiency. Inengineeringunits, specific impulse is given in(pounds-force * seconds)/pound-mass. A thor-oughyet succinct discussionof the physicsandthermodynamics of rocket propulsionisfound in Sutton.fThe prediction of rocketpropellant specificimpulse, as well as impulse under otherconditions, maybereliablyaccomplishedbycalculationusingasinputthechemical com-position, theheat of formation, andtheden-sityof thecomponent propellant chemicals.Not only impulsebut also the compositionofexhaust species (andof species inthecom-bustion chamber and the throat) may becalculated ifthe thermodynamic propertiesof thechemical species involvedareknownor can be estimated. The present standardcomputer code for such calculations isthat described by Gordon and McBride.44Theoretical performance predictions usingsuch programs are widely used to guidepropellant formulation effortsandtopredictrocket propellant performance; however, veri-fication of actual performanceis necessary.TYPESOFPROPELLANTSThetwoprincipal typesof rocket propellantin general use are solid propellants and liquidpropellants. Solid propellants are chemicalcompositions that burnonexposedsurfacesto produce gases for rocket power. Liquid pro-pellantsrely onpumpingor pressurizedflowof storedliquidstothecombustionchamber.Thechoicebetweensolidandliquidpropel-lantsforaspecificapplicationdepends onavariety of considerations;to date, many of thestrategic missiles and most of the tacticalmissilesrelyonsolidpropellants becauseofthe lowercost of therocket andthegreaterstorability of the propellant. On the otherhand, large spacevehicles androckets firedfor maneuveringinspaceuseliquidpropel-lants, inpart becauseof thereadycontrolla-bility of liquidsystems. Less widelyused arehybrid rockets, which use solid fuel and liquidor gas-phase oxidizer. Ifa single chemicalcompound (e.g., nitromethane) containingbothoxidizingandreducingfunctions inthesame molecule is employed to power a rocket,CHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1171it is called a monopropellant. Iftwo chemicalscombineto provide the propulsion, they forma bipropellant system.SOLIDPROPELLANTSA solid propellant rocket motor is quitesimple in concept, although in practice a com-plete motor is more complex. As shown inFig. 37.15, therocketpropellantis containedwithin a case, which may be metal or areinforced high-performance composite.Frequently, the case is internally shielded by abondedlayerof insulation. Theinsulationiscoated with a liner that bonds the propellant tothe insulation. Theintegrity of the propellant-to-linerbondis of utmost importance; failureat this interface during a motor firing canresult in a sudden increase in the area ofpropellant surface exposed to combustion,with potentiallycatastrophic results.The bore or perforation ofthe propellantgrainis a major factorin determining the bal-listic performance of a rocket.In the simplestinstance, the grain has no perforation, and theburning isrestrictedtotheendof thegrain;the resultingend-burning rocketshave a rela-tivelylongburningdurationwithlow thrust.More commonly, a perforation extendsthrough the grain (center-perforated) and mayhave a cylindrical , star, cross-shaped, wagon-wheel, or other more complex profile. Theconfigurationof thegrainisusedtocontrolthe burning behavior ofthe propellant; themoresurfaceareathereis exposed, themorerapidly propellant will be consumed, affectingperformanceover time. Thelengthof timearocket motor will bumisgovernednotonlybytheperforationgeometry, but alsobytheweb thickness of the propellant (distancefrom perforationto liner), the burningrate ofthe particular rocket propellant,and the throatdiameter of the nozzle. The pressure-timecurve resultingfrommotor burning maybeneutral (a single pressure is achieved andmaintainedthroughout the bum), progressive,or regressive. Progressive burning leads toacceleration, whereas regressive burninggiveslower pressureasthefiringprogresses.Tactical solid propellant motors frequently aremanufactured withtwo types of propellant: arapid-burning boost propellant to provide ini-tial accelerationand a slower-burningsustainpropellant to completethe desiredflight pro-file. The trajectory of missiles as a function ofpropellant properties,grain configuration, andmissile design maybe reliablypredictedorsimulatedby sophisticated computer calcula-tions. A typical tactical solid propellant-basedmissileis shown in Fig. 37.16.Single and Double-Base Propellants.Earlysolidrocket propellants werebasedonprocessingmethods similar to that used in therubber industry, with propellants extruded intothe desired grain configuration. PropellantsPerforation (Bore)CasePropellant GrainFig. 37.15. Asolidpropellant rocket motor.1772 KENTANDRIEGEL'S HANDBOOKOF INDUSTRIALCHEMISTRYANDBIOTECHNOLOGYFig. 37.16. Solidpropellant-basedHAWK tactical missile.that havebeensuccessfullymanufacturedbythis technique includenitrocellulose (single-base) andnitrocellulose-nitratoester (double-base) materials. * Double-base propellantscontain both nitrocellulose and NGas theprincipal components; additionally, chemicals*Triple-base propellantshave also been produced, hav-ing double-base composition plus nitroguanidine,added as a combustion coolant or as a ballistic modifier.suchas stabilizers, plasticizers, andburningratemodifiersmaybeaddedasappropriate.Other nitratoesters also may be in double-basesystems. Extruded propellants usually are lim-itedtosmall graindiameters ...m X "'I:l5 (I) 2 C ::xJo n ;;0;:m -I"'I:l::xJo "'I:lm ......> 2 -I(I)Fig.37.20.EngineschematicfortheTitanIVStageI(LR87-AJ-II).(CourtesyAerojetPropulsion).........00...1782 KENTANDRIEGEL'SHANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYTABLE 37.6 Properties of Common Liquid PropellantsHeat ofFreezing Boiling Critical Critical Formation HeatofMolecular Point Point Temp. Press. Specific (cal/mol e Vapor.Propellant Weight (F) (F) ( F) (psia) Gravity at 298.16 K) (BTUllb: NBP)L0232.0 -362 -297 - 182.0 730.6 1.14" -2,896 91.62F238.0 -365 -307 -201 808.5 1.50" -3,056 71.5NP492.011 11.75 70.4 316.8 1,441.3 1.45b-4.7 178.2CIFs130.445 -153.4 7.3 289.4 771 1.795b-60,500 76.04H20234.016 31.2 302.4 855 3,146 1.38b-44,750 76.04H22.016 -434.8 -423.3 -399.9 188 0.071" - 1,895 195.3Nll432.045 34.75 237.6 716 2, 131 1.008b12,054 583MMH 46.072 - 62.3 189.8 594 1,195 0.879b13,106 377UDMH 60.099 - 70.94 144. 18 482 867 0.785b12,339 250.6A-50 41.802 22.0 158 633 1,731 0.905b12,310 346.5(50% N2Hc50% UDMH)RP-I (H/C = 2.0) 172.0 - 55 422 758 340 0.807b-6,222 125Hp 18.016 32 212 705.43,206.2 1.0b- 68,317 970.3"Evaluated at NBP; 'Evaluated at 68F (293.4 K).operating range and a large payload capacity, thedesired physical propert ies are: lowfreezingpoi nt low temp erature variability lowvapor pre ssure highspecificgravity highheatsoffor mationand vaporizationBecauseliquidpropellantsmayalsobe usedto cool the thrust chamber ass embly, goodheat transfer propert ies, suchas highheat ofvaporization, highthermal conductivity, highspeci fic heat, and high boiling poi nt , aredesirable.LiquidOxidizers. Liquidoxidizers can becategorized as either storable or cryogenic.Manydifferent types of liquidoxidizers havebeenusedinchemical propulsionsystems. Ingeneral , cryogenics such asliquid oxygen, fluo-rine, orfluorinated compoundsgivea highspe-cific impulse. Several storable oxidizerssuch asnitrogentetroxide(N204) , inhibitedredfumingnitricacid(IRFNA), or chlorinepentafluoride(ClFs)have beenused for their advantages instorage . Abriefdescriptionofthe commonlyused oxidizers is given below.Cryogenics. Liquid oxygen, the mostimpor tant andextensivelyusedliquidoxidizer,is usedprimarily with liquid hydrogento give averyhighspecificimpulse(usually near or over400lbf-sec/lbm), Major applications of theliq-uid oxygen and liquid hydrogen bipropellantsysteminclude the space shuttle mainengineand the Saturn second stage engine (1-2). Liquidoxygen is alsowidelyusedwithhydrocarbonfuelsintheboosterengineofheavyliftlaunchvehiclessuch astheRussianEnergia. Althoughliquidoxyge ncanbeusedwithstorablefuels,such as hydrazine or monomethylhydrazine(MMH), this bipropellant combination engine isstill in the development stage, mainl y because ofthedifficultyof chambercoolingandcombus-tionstabil ity.Both the freezing point(-362F, 54.5K)andtheboiling point ( - 297F, 90K) ofl iquidoxygenare low, permittinga wide rangeofoperat ion. Liquid oxygen is highl y react ivewi thmost organic mat erialsina rapidlypres-sur ized confine ment region of rocket combus-tionchambers. Except for therelati velyhighevaporation rate, the handl ing and storageproblems for liquid oxygen are min imal.Although liquid oxygen is notconsidered cor-rosiveandtoxic, thesurfaces that wi ll be incontact withthe liquidoxygenmu st be keptextremelyfreeofanycontaminati onbecauseof its reactivity. Thelow boiling point also cancause problems due to low temperatureCHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1783embrittlement. In order to minimize oxidationproblems,metals such ascopper are used.Storage tanks and transfer lines ofliquidoxygen systems must be wellinsulated to pre-vent thecondensation of moistureorairwithsubsequent ice formation on the outside.Vacuumjackets, formed plastics, and alter-nate layers of aluminumfoil andglass-fibermats havebeen used successfully.Liquid fluorineand fluorinecompounds (F2,OF2,or NF3)are also cryogenic oxidizers.Although fluorineoffers specific impulse anddensityadvantages,extreme toxicity andcor-rosiveness have prevented the practicalapplicationof fluorine and fluorinatedcom-pounds in chemical rocket design. In addition,with fluorine the handlingproblemsare sig-nificant because fluorinehasthehighest elec-tronegativity, hence reactivity, of anyof theelements-plus a very low boiling point(85K), necessitating extensive facility sup-port requirements.Storable. Nitrogen tetroxide and IRFNA arethemost important andmost extensivelyusedstorable liquid oxidizers. A high density yellow-brown liquid, nitrogen tetroxide is very stable atroomtemperature, existing as an equilibriumwith N02(N204f- f- 2N02), with the degree ofdissociation varying directlywith temperatureand indirectly with pressure. At atmosphericpressure androomtemperatureN204containsapproximately 15 wt. %N02,but at 303F(423 K) it is essentiallycompletelydissociatedinto nitrogendioxide. Upon cooling, nitrogentetroxide dimer is re-formed. lt is used as the oxi-dizerfor the Titan first andsecondstage rocketengines, Delta second stage rocket engine, for theorbital maneuvering engines of the space shuttle,plus finds use in divert and attitude control(DACS) military and civil applications.Thefreezing temperature of nitrogen tetrox-ide (11. 75F, 262K) is relatively high, so caremust betaken toavoidfreezing(causing flowblockage) whenever it is used. For this reason,nitricoxide(NO) maybeadded (applicationswith as much as 30 wt. %NO, as mixedoxidesof nitrogen(MON), havebeennoted)tothenitrogentetroxidetodepressthefreez-ingpoint, improvingspace-storability of thisoxidizer. Additionally, with 1-3 wt. %NO,storability in titanium tanks is greatlyimproved, due to reduced stress corrosionover time. Nitrogen tetroxide itself is notcor-rosiveif pure, that is, if themoisturecontentisverylow.Carbonsteels, aluminum, stain-less steel, nickel, and Inconel can be usedwithit. However, whenthe moisturecontentincreases aboveabout0.2 wt. %, thenitrogentetroxide becomes increasingly corrosive, and300-series stainless steel should beused.IRFNAconsistsof concentrated nitric acid(HN03)thatcontains dissolved nitrogen diox-ide and a small amount offluoride ion, ashydrofluricacid(HF).The addition ofHF provides the fluorideion, whichreacts withthe metal containers,forming a metal fluoridecoating and reducingthecorrosivenesssignificantly. Aswithnitro-gen tetroxide, IRFNAis mainly used withhydrazine-typefuels inbipropellant systems.Because nitric acid ignites spontaneouslywithanilineandamines(hypergolicity), caremust be taken in handling and storing theIRFNA. However, thisis anadvantagein sys-temswhere extinguishment andreignition aredesired.MONand high density acid (HDA) arevariantsof storableoxidizers basedondini-trogentetroxide. The MONpropellantscon-sist ofN204and NO, as noted earlier, andHDAis a mixture ofnitric acid and N204.Both HDA and MONbehave similarly toIRFNA.Other liquidoxidizers, suchasconcentrated(usually >70 wt. %) hydrogen peroxide(H202), chlorine trifluoride (ClF3),and Clf', areusedasrocket propellantsfor special applica-tions. CIF3and CIFs can behighlycorrosivetometals. Otherinterhalogen compounds suchasCI03F, CIF30, or BrFs can also be considered asalternatives. Rocket-grade hydrogenperoxide,recentlyavailablein quantityatconcentrationsover 98 wt. %via the anthroquinone process,isgainingwidespreadrespect as a"green"pro-pellant option. However, hydrogen peroxide hasserious shortcomings in its incompatibility withawiderangeof possiblecontaminants, whichhave resulted in catastrophic failure of lines andtanks in extended storage scenarios. Booster1784 KENTANDRIEGEL'S HANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYFig. 37.21. A200-f (60-m) longflameshootsout fromtheSeal Aerospacesecondstageengineduringatest firing March 4, 2000. Theengine issupposed to produce810,0001bof vacuumthrust, usinghydrogenperoxideandkerosenepropellants.(Photocourtesy of Beal Aerospace.)applications have demonstrat ed, in static test fir-ings, capabilities for high-performanceheavylift launchvehicles usingH20/kerosenepro-pellants as shown in Fig. 37.21.LiquidFuelsCryogenic. Liquid hydrogen, the most impor-tant and widely used liquid fuel, is used mainlywith liquid oxygen to give high performance, asmentioned above. Liquid hydrogen has excellentheat transfer characteristics: high heat of vapor-ization, high specific heat, and high thermalconductivity. Itis a very good choice to cool thethrust chamber assemblywhenit isusedinaregeneratively cooled system. However, the lowboiling point (-434.8F, 14 K) andlow densityofliquidhydrogenmakeit difficulttohandleandstore. Thelowfuel densitymeansthat avery large and bulky fuel tank is required; this isconsidereda disadvantage when a high ratio ofpayload to vehicle dry weight is desired. Liquidhydrogenhasbeenfoundtoreact withmetals,causing embrittlement of such metals as nickel.Copper is the best and most widely usedmaterial for liquidhydrogeninrocket engineapplications.As with liquid oxygen , storage tanks andtransfer lines of liquid hydrogen systems mustbewell insulated, toprevent theevaporationof hydrogenor condensation of moistureorairwithsubsequent iceformationontheout-side. Vacuumjackets, formed plastics, orglass-fiber mats mixed with aluminumfoilcanminimizetheproblems.Molecular hydrogen exists in two forms:ortho-hydrogen(nuclei of thetwo atomsspin-ningin the same direction)and para-hydrogen(nuclei of thetwoatoms spinninginoppositedirections). These two forms are in equilibriumwitheachother, andat roomtemperature theequilibrium mixture contains75 percentof theorthoformand25percent of thepara form.Upon cooling to the normal boiling point(-425F, 20.4 K), the equilibriumis shifted.At thistemperature, theortho formwill con-vert slowlytothe para form. Theequilibriumconcentration ofpara-hydrogen at this temper-ature is 99. 8 percent. (The shift of theortho-para equilibriumproduces energy thatcauses a liquid hydrogen storage problem.)Therefore, para-hydrogengenerallyis usedasliquid fuel for rocket engine appl ications.Modernliquefiers can produceliquid hydrogenthat is more than 99 percent para-hydrogen.50Liquid methane (CH4) , another kind ofcryogenic fuel usedin testing and experiment,generally is used with liquid oxygen in abipropellant system. It hasthe advantageofa considerably higher density than that ofhydrogen(thespecificgravityformethaneis0.4507 at (-258.7F, 111.7k) the normalCHEMICALEXPLOSIVESANDROCKET PROPELLANTS 1785boilingpoint). To datenooperational rocketengineutilizesliquidmethane as thefuel;allliquid oxygen/liquid methane enginesare stillin the development stage.Storable. Together with liquid hydrocarbons,hydrazine-type fuels are the most important stor-ableliquid propellants. Theyinclude hydrazine(NzH4) , MMH, unsymmetrical dimethylhydrazine(UDMH), Aerozine-50(50%NzH4and 50%UDMH), and various blends of these fuels withotheramine-based components. All hydrazine-type fuels are toxic tosome degree, as are theirbreakdownproducts intheenvironment (espe-cially, as in the caseof diluteUDMHwithnitratesandnitrites, formingcarcinogenic andhighlywater solublenitrosodimethylamine, orNDMA).The most notablehydrocarbon storablefuelsinclude kerosene-based liquid propellants(RP-I,JP-8, and others).Acolorless liquid, hydrazine is stable toshock, heat, andcold. The freezingpoint ofhydrazine (34.75F, 274.9K) is the highestof commonly used hydrazine-type fuels.Because it starts to decompose at 320F(433 K)withnocatalystspresent, itis unde-sirableforuse as thecoolant for regenerativecooling of the thrust chamber. Differentblends of hydrazine and MMH have beentested to improve heat transfer properties.Hydrazineisgenerallycompatiblewithstain-less steel, nickel, or aluminum. (See Chapter 22for moreinformation on hydrazine.)UDMHis neither shock- norheat-sensitive,andit isastable liquideven athightempera-ture. A key advantage is its low freezing point(-71F). Furthermore, it is compatible withnickel, Monel, andstainless steel. UDMHisoften used as rocket propellant mixed withhydrazine in various proportions. A 50/50 mix-turewithhydrazine, Aerozine-50, isusedforthecurrent DeltaIIStage2. Anecdotally, theTitan IV vehicle fly-out (last flight) occurred inOctober 2005 with vehicle B-26, a "black"mission with a satellite for the NationalReconnaissanceoffice (NRO) engines.MMHfuel isgenerallyusedwithnitrogentetroxide (NZ04) oxidizer insmall spacecraftrocket enginessuch as orbital maneuvering oraltitude control engines. Compared tohydrazine, MMHhasbettershockresistanceand better heat transfer properties as acoolant. However, the specific impulse forMMH/Nz04 engines is slightly lower than thatfor hydrazine/Njo, bipropellant engines.Likehydrazine, MMHis compatible withstainlesssteel,nickel,aluminum, Teflon, and Kel-F.Ingeneral, thehydrazine-typefuelsdonothave very good heat transfer properties.Therefore, in the latest development of ahigh-pressure bipropellant system using NZ04andhydrazine-typefuels, the oxidizer Nz04has been used as a regenerative coolantinstead of the fuelitself.Monopropellants. Simplicityand low costare the major reasons why monopropellantrocket engines are considered for developmentand deployment. The specific impulse formonopropellant engines generally is muchlower thanthat for bipropellant engines (inthe rangeof 200 lbf-sec/lbm for monopropel-lant vs. 280-400 lbf-sec/lbm for bipropel-lant). Hydrazine is the most important andwidelyusedmonopropellant insmall trajec-torycorrection oraltitudecontrol rockets. Inan effort to lower the freezing point forimprovedstorability, manyhydrazine blendshave been studied."Hydrogen peroxide has been used as a mono-propellant, especiallyinvarious-concentrationsolutions with water. It was used as a rocket pro-pellant in the X-IS research aircraft. Current useof rocket-gradehydrogenperoxide, or "high-test" peroxide (HTP-generally greater than90% concentration in water) as a monopropel-lant is in thedevelopmental stages, mostly forstation-keeping on orbit, or as an oxidizer-com-patible pressurant gas source.5Z,53 Long-termstorability ofhighly concentrated hydrogen per-oxide is still problematic, although recentadvancesinorientedcrystallinepolymersandother novel compositesshow greatpromiseinlightweight yet compatible tankage materials.Gelled Propellants. As with powderedmetallicfuelsinsolidcomposite propellants,early interest in gelled liquid propellantsfocusedon gelationas a meansof incorporat-inghigh-energysolidsintoliquidpropellants1786 KENTANDRIEGEL'SHANDBOOKOFINDUSTRIALCHEMISTRY ANDBIOTECHNOLOGYtoachievehighspecificimpulseanddensity.Storable hydrazine-type fuels such ashydrazine and MMH have received most oftheattentionin gelationdevelopment. Duringthedevelopment ofTitan IIA*, a stable suspensionof aluminumpowder in gelled hydrazine(calledAlumazine) wasdevelopedandtestedextensively. Later the needsfor such a vehicledisappeared, leaving the gelation technology tolanguish for lack of other applications.In the early 1980s, an increasing focuson improving the safety and handlingcharacteristics ofstorable liquid propellantsrevivedtheinterest indevelopinggelledliq-uid propellants. Although gelation technologyfor bothcryogenicandstorableliquid propel-lantshasbeendeveloped, most of theactivi-ties have concentrated on storable propellants,especially in liquid fuels. Comprehensivereviewscoveringall gelledfuels developmentactivities canbefoundinreferences 54and55. A brief description of the gelledfuels andoxidizersis given below.GelledFuel. Gelledfuels generallyhaveconsisted of metallic powders such as aluminumor boron, or carbon black plus other polymericgelants, suspended in MMH or an MMH-blendfuel. These gels are typically applied to tacticalmissileapplications.Thegelledfuelswithoutmetal additiveshavedrawnaddedinterest aspropellantswithminimumorreducedexhaustsignatures and relatively high specific impulse.Gelled fuelshaveessentially thesametox-icitiesas theirungelled counterparts becausegelationdoes not significantlychangetheircompositionsorequilibriumvaporpressure.However, the rates of vaporization aredecreased significantly, reducing the toxicexposure hazards. Gelled fuels, such asgelled MMH, are hypergolic but can burnonlyupondirect contact of thefuel gelwithoxidizer; thefire hazardsaregreatly reducedwith respect to both intensity and extent.Compatibility of thegelledfuelsgenerally isthe same as those of the ungelledfuels as*TitanIutilized keroseneandLOX aspropellant; theTitan II ICBMdevelopment required earth-storablepropellant selection.regards materialsof tankage."There isevi-dence, however, that selectedfillers or gelloadingsin MMHhave caused inordinate off-gas and pressure increase over time withthese tactical fuel gels; ongoing studiesareunderway to identify and minimize thispotentialincompatibility in storage.Gelled Oxidizers. Development work ongelledoxidizerswas startedduringthe 1960s,butvirtually no effort was expended on them duringthe 1970s. Development work was revivedin the1980s as interest in gels was awakenedbecauseof their improved safety and handling character-istics. Gelled oxidizers include nitrogen tetrox-ide, MON, red fuming nitric acids (RFNA),andIRFNA.The gellingagents used for the oxidizersinclude powdered lithium nitrate (LiN03) ,lithiumfluoride (LiF), plastisol nitrocellulose(PNC), andcolloidal silica. Theearly work onthese gels can be found in references 57 and 58.For tactical applicationswith minimum exhaustsignatures, gelled IRFNA and CIFs are the pri-mary gel oxidizers.Likethegelled fuels, the toxicity of gelledoxidizers is not reduced, but the handlingand safety hazards of storage are greatlyimproved. Gelled IRFNAis considered to becompatible with aluminum. Recent effortshaveshownthat itcanbestoredforat leastas long as the non-gelled IFRNA. Studiesat UAHinthis country(sponsoredbytheU.S. ArmyMissileCommand) and Universityof Nottingham(sponsored by the UnitedKingdom's Royal Ordnance) have identi-fiedmechanisms and additivestoincreasestorability of gelled IRFNAand analogs;their deployment, however, is yet to be seen.ADVANCEDMONOPROPELLANTSTUDIESHAN, ADN, AN, HNF, HTP: Monopropellants(and oxidizer) Alphabet Soup Studies ofhydrazine-family replacements, in this contextincluding hydrazine, methylhydrazine, andunsymmetrical dimethylhydrazine, areincreasingly justified based on decreasingtoxic limit exposures and associated highercost for storage and deployments of theseCHEMICALEXPLOSIVES ANDROCKET PROPELLANTS 1787propellants as both mono- and bi-propellants."As monopropellant, hydrazine has increasedcompetition from water-based ionic liquidblends that toa largedegreeincludehydroxy-lammonium nitrate (HAN, NH30HN03),ammoniumdinitramide(ADN, NH4N(N02)2),or ammoniumnitrate (AN, NH4N03),and to alesser degree includes hydrazinium nitrate (HN,N2H5N03),hydraziniumnitroformate (HNF,N2H5C(N02)3),orperhaps hydrogenperoxide(HTP, H202).60-{;4Blendsof thesecompounds,withor without ionicormolecularfuels,havebeenstudied for their applicabilityas gun pro-pellants or monopropellants to varying degrees,without significant fieldeddeployments asofthis date ofwriting. The predominant issuesthatprevent wideracceptanceof thesepropel-lants include high combustion temperatures(ontheorderof 2000+ Cversus 1100Cforhydrazine), reliable performance with heteroge-neous catalysts(typicallyiridiumonaluminasupport), and their storability and compatibilitywith typical materials of construction.Inaseries of gas-generatingcompositionsalsohaving utilityas monopropellants, U.S.Navy investigators report the PERSOL,OXSOL, PERHAN-family water-basedblends using H202/AN/H20,H20/HN/H20(PERSOLs), HN/AN/H20(OXSOLs), orH202/HAN/H20(PERHANs).65-68 Theversa-tilityof these blends offer not onlyreducedtoxicity as compared to hydrazine replace-ment monopropellants, but alsoas oxidizersinbipropellantorhybridpropulsionsystems.Alternative applications may even includebreathablegasgenerationoruseasanoxygensource for welding. Theseternary blends areunique also in their low freezing points (as lowas - 50C) and relatively high densities(1.3-1.6g/cc or greater) which make themattractive as improved performance optionsregardless of their reducedtoxicitypotential.However, asinthecaseforHTPorHANuseelsewhere, storage stabilities and potentialincompatibilities due to fume-off when inadver-tently contaminated by decompositioncatalystsmay maketheir use problematic. Work in gov-ernment andindustrylabsisongoingin theseareas in search ofrisk mitigation for use oftheseadvanced mono- and bipropellant materials.BIPROPELLANT APPLICATIONSThe ongoing search for reduced toxicrtyand improved performance in both mono-andbipropellants is driven by cost factors andinfrastructure concerns as noted above, butalso inprograms such as the U.S. nationaleffort Integrated High Payoff RocketPropulsion Technology (IHPRPT)69 multi-phasedgoals. Inour context ofpropellantsand their ingredients, the IHPRPT goals are todoubletheperformance of rocket propulsionsystemsover thecurrentstateof theart, andto decrease the cost ofaccess to space forboth commercial and military sectors.Predominant amongthe applications for thesehigh-payoff improvementsin propellants,theboost andorbit transfer segment is amajorbeneficiary, withspacecraftandtactical (i.e.,defense) segments receiving a lesserbenefit.BIPROPELLANTFUELSWith many of the oxidizers discussed above intermsof useasmonopropellants, blendswithionic and molecular fuels are noted to improvetheir performance, at theexpenseof hazardsratings or storage instabilities. Examples ofionic fuels intended for use as blends in mono-propellants include tris( ethanol)ammoniumn