BookChapter_Rocket Propellants and Chemical Exp

37

Chemical Explosives andRocket Propellants

Walter B. Sudweeks, * Felix F. Chen,** and

Michael D. McPherson**

PART I. CHEMICAL EXPLOSIVES

INTRODUCTION

The average citizen in today's world giveslittle thought to the important role that commercial explosives play in our lives and howtheir 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.

To maintain our standard of living in theUnited States, every day 187,000 tons of concrete are mixed, 35 million paper clips arepurchased, 21 million photographs are taken,using large quantities of silver, 80 pounds ofgold are used to fill 500,000 cavities, and 3.6million light bulbs are purchased. It takes

*Consultant, Part I, Chemical Explosives . The authorwishes to acknowledge that this section is an updateof the corresponding material in the tenth editionauthored by Boyd Hansen.**Aerojet Propulsion Division. Part II, RocketPropellants.

1742

more than 40 different minerals to make atelephone, and 35 to make a color television .Even everyday products such as talcum powder, toothpaste, cosmetics, and medicinescontain minerals, all of which must be minedusing chemical explosives. I

Without explosives the steel industry andour entire transportation system would not bepossible. The generation ofelectricity has beenlargely dependent on coal, and coal miningtoday is still the largest consumer of industrialexplosives. Rock quarrying for road buildingand excavations for skyscrapers, tunnels,roads, pipelines, and utilities are direct beneficiaries of the labor-saving use of explosives.

COMMERCIAL EXPLOSIVES MARKET

The use ofcommercial 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 Survey

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1744 KENT ANDRIEGEL'S HANDBOOK OF INDUSTRIAL CHEMISTRY AND BIOTECHNOLOGY

TABLE 37.1 Industrial Explosives and Blasting Agents Sold in the United States byState and Class (Metric Tons)

2002 2003

Fixed High Explosives FixedHigh Explosives

Other Blasting Other BlastingHigh Agents and High Agents and

State Permissibles Explosives Oxidizers Total Permissibles Explosives Oxidizers Total

Indiana 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 25,095 953,198 978,351

Total 1,360 38,100 2,470,000 2,510,000 1,070 35,500 2,250,000 2,290,000

Note: Data rounded; may not add up to total shown.Source: IME.

(USGS) and the Institute of Makers ofExplosives (IME) from 1994 to 2003.2,3 Figure37.1 also separates the volumes by industryuse. The open-pit coal mining industry continues to be the largest user, as it has been formany years. Table 37.1 shows the commercialexplosive usage by seven leading states for2002 and 20m? In the year 2003, the fourstates consuming the most explosives (indecreasing order) were: West Virginia,Kentucky, Wyoming, and Indiana, all coal mining states. The coal market is also slowly making a shift from the eastern states to the westernstates with lower BTU, but more importantly,lower sulfur coal. Through the 1990s thesparsely populated state of Nevada ranked inthe 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 efficiencies of scale to overcome theoverall lower grade of ore, the same transformations that other metal mines had madedecades before. Along with this change in mining style came a conversion from small diameter packaged explosives such as dynamite tolarge, bulk explosive loading systems usingemulsions and ammonium nitrate/fuel oil(ANFO).

CHEMISTRY OF COMBUSTIONAND EXPLOSION

For a simple understanding of 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 ignition. The process of combustion is basicallyanoxidation-reduction (redox) reactionbeween the fuel and oxygen from the air. Onceinitiated, this reaction becomes self-sustaining and produces large volumes of gases andheat. The heat given off further expands thegases and provides the stimulus for the reaction to continue.

The burning reaction is a relatively slowprocess, depending upon how finely dividedthe fuel is, that is, the intimacy of contactbetween the fuel and the oxygen in the air.Because burning is diffusion-controlled, themore intimately the fuel and oxygen aremixed, the faster they can react. Obviously,the smaller the particles of fuel, the faster thecombustion can occur.

Another result of the fineness or particlesize of the fuel is the completeness or efficiency of the reaction. In a complete combustion all the fuel elements are oxidizedto their highest oxidation state. Thus, wood,

CHEMICAL EXPLOSIVES AND ROCKET PROPELLANTS 1745

OXIDIZER

Fig. 37.2. An explosion triangle.

Oxidation-Reduction- gases + heat(fast)

N--_..... SOURCE OFIGNmONFUEL

It should be noted that an explosion differsfrom ordinary combustion in two very significant ways. First, oxygen from the air is not amajor reactant in the redox reactions of mostexplosives. The source of oxygen (or otherreducible species) needed for reaction with thefuel-the oxidizer-may be part of the samemolecule as the fuel or a separate intermixedmaterial. Thus an explosive may be thought ofas merely an intimate mixture of oxidizer andfuel. This degree of intimacy contributes to thesecond significant difference between anexplosion and normal combustion-the speedwith which the reaction occurs.

Explosives in which the oxidizer and fuelportions are part of the same molecule arecalled molecular explosives. Classical examples of molecular explosives are 2,4,6- trinitrotoluene (TNT), pentaerythritol tetranitrate(PETN), and nitroglycerin (NG) or, more precisely glycerol trinitrate. The chemical structures of these explosives are shown in Fig. 37.3.As can be seen in the structures, the oxidizerportions of the explosives are the nitro (-N02)

groups in TNT and the nitrate (-ON02) groupsin PETN and NG. The fuel portions ofall threeexplosives are the carbon and hydrogen (C andH) atoms. Comparison of the ratios of carbonto oxygen in these explosives (i.e., approximately 1 : I for TNT, approximately 1 : 2 forPETN, and 1 : 3 for NG) shows that TNT andPETN are deficient in oxygen; that is, thereis insufficient oxygen present in the molecule to fully oxidize the carbon and hydrogen. Consequently, products such as carbonmonoxide, solid carbon (soot), and hydrogenare produced, as well as carbon dioxide andwater vapor. Prediction of the exact products of

being mainly cellulose , and gasoline , beinggenerally a hydrocarbon (e.g., octane), produce primarily carbon dioxide and watervapor upon complete combustion. Once initiated these burning reactions give off heatenergy, which sustains the reactions. Heat isreleased because the oxidized products of thereaction are lower in energy (more stable)than the reactants. The maximum potentialenergy release can be calculated from therespective heats of formation of the productsand reactants. Actual heats of combustioncan be measured experimentally by causingthe reaction to occur in a bomb calorimeter.The calculated energy values for the abovereactions are - 3,857 cal/g for cellulose and- 10,704 cal/g for octane, respectively.

In the case of an inefficient burn , some lessstable or higher-energy products are formedso that the resultant heat energy given off islower than that for complete combustion. Inthe above examples inefficient combustioncould result from lack of oxygen accessibility, producing carbon monoxide or even carbon particles instead of carbon dioxide. Asmoky flame is evidence of unburned carbonparticles and results from inefficient combustion where fuel particles are so large orso dense that oxygen cannot diffuse to theburning surface fast enough. If this inefficiency is great enough, insufficient heat isgiven off to keep the reaction going, and thefire will die out.

All chemical explosive reactions involvesimilar redox reactions; so the above principles of combustion can help illustrate, in avery 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, which is similar to the fire triangle .In general, the products of an explosion aregases and heat although some solid oxidationproducts may be produced, depending uponthe chemical explosive composition. As innormal combustion , the gases produced usually include carbon dioxide and water vaporplus other gases such as nitrogen , againdepending upon the composition of the chemical explosive.

1746 KENTANDRIEGEL'S HANDBOOK OF INDUSTRIAL CHEMISTRY AND BIOTECHNOLOGY

TNT PETN NGON02

CH3I CH2-0N02CH2

02NIQrN02 I I°2NO-H2C-C-eH2-0N02

I CH-ON02H H CH2 II

N02 ON02 CH2-0N02

Fig. 37.3. Chemical structure of three molecular explosives.

explosion is complex, especially for the oxygen-deficient explosives, because the ratios ofcOz, CO, HzO, and Hz will vary, dependingupon reaction conditions (explosive density,degree ofconfinement of the explosive, etc.).4,S

The following equations show typical idealreaction products along with calculated heatsof reaction for these molecular explosives:

C7HsN306 ~ 1.5COz + 0.5CO + 2.5HzOTNT + 1.5Nz + 5C + 1290 callg

CsHgN401Z ~ 4COz + 4HzO + 2Nz + C

PETN + 1510 callg

what is needed for complete combustion ofthe fuel elements) or oxygen deficiency(compared to the amount required forcomplete combustion). It is expressed aseither a percentage or a decimal fraction ofthe molecular weight of the oxygen in excess(+ ) or deficiency (- ) divided by the molecular weight of the explosive or the ingredientbeing considered. Individual componentsof an explosive mixture have O.B. valuesthat may be summed for the mixture.Shown below are the O.B. calculations forAN and FO:

FO

Mol. wt. = -14n

+(112)(32)O.B. = 80 = +0.20

- (3n/2)(32)O.B.= 14n =-3.43

Mol. wt. = 32AN

Mol. wt. = 80

From the O.B. values, one can readilydetermine the ratio of ingredients to give azero O.B. mixture for optimum efficiency andenergy. Thus the weight ratio for ANFO is94.5 parts of AN and 5.5 parts of FO(94.5 X 0.20 = 5.5 x 3.43).

For the molecular explosives shown previously, 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 callg

Explosives in which the oxidizer and fuelportions come from different molecules arecalled composite explosives because they area mixture of two or more chemicals. A classicindustrial example is a mixture of solidammonium nitrate (AN) and liquid fuel oil(FO). The common designation for this explosive is the acronym, ANFO. The oil used (typically #2 diesel fuel) is added in sufficientquantity to react with the available oxygenfrom the nitrate portion of AN. The redoxreaction ofANFO is as follows:

3NH4N03 + -CHz-AN FO

~ COz + 7HzO + 3Nz + 880 callg

"Oxygen balance" (O.B.) is the termapplied to quantify either the excess oxygenin an explosive compound or mixture (beyond


PETN is only slightly negative; but TNT isvery negative, meaning significantly deficientin oxygen. Therefore, combinations of TNTand AN have been employed to provide additional oxygen for the excess fuel, as, forexample, in the Amatols developed by theBritish in World War 1.6

Modem commercial explosives react in avery rapid and characteristic manner referredto 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, and liberation of energy.This energy, in tum, continues to drive theshock wave. Pressure in a detonation shockwave may reach millions of pounds per squareinch. The sudden pressure pulse shocks theexplosive material as it passes through, causing a nearly instantaneous chemical reactionin the body of the explosive. Once initiated,molecular explosives tend to reach a steadystate reaction with a characteristic detonationvelocity. Composite or mixture explosivesalso have steady-state detonation velocities,but these velocities are more variable thanthose of molecular explosives and are influenced by such factors as diameter of thecharge, temperature, and confinement.

HISTORICAL DEVELOPMENT

The first known explosive material was blackpowder, a mixture of potassium nitrate(saltpeter), charcoal, and sulfur. As such it is acomposite explosive whose properties aredependent upon how finely divided each ofthe ingredients is, and how intimately they aremixed. The exact origins of black powder arelost in antiquity. Publications referring to itseem about equally divided between those thatattribute its origin to third- or fourth-centuryChina" and those that place it closer to the13th century, at about the time of RogerBacon's written description in 1242.9

-13

Nevertheless, its use did not become verypopular until the invention of the gun by

Berthol Schwartz in the early BOOs; and itsfirst recorded use in mining did not occur forover 300 years after that. First used for blasting in 1627, the production and application ofblack powder played a critical role in the rapidexpansion of the United States in the early19th century as canals were dug and railroadsbuilt to span the continent.

For over 200 years black powder was theonly blasting agent known, but the 1800sbrought a number of rapid developments thatled to its demise, replacing it with safer andmore powerful explosives. Table 37.2 presentsa chronological summary of some of the significant discoveries of the 1800s. Credit forthe first preparation of NG is generallyascribed to Ascanio Sobrero in Italy in 1846.

Swedish inventors Emmanuel Nobel and hisson Alfred took an interest in this powerfulliquid explosive and produced it commercially in1862. However, its transportation and its handling were very hazardous, and eventuallyAlfred Nobel discoveredthat NG absorbed intoa granular type of material (kieselguhr) wasstill explosive, but was much safer to handleand use than the straight liquid. This newinvention, called "dynamite;' was difficult toignite by the usual methods used for pure NG.Therefore, also in 1867, Alfred Nobel devisedthe blasting cap using mercury fulminate. Withthis development dynamite became the foundation of the commercial explosives industry.

For military and gun applications blackpowder continued to be the only explosive of

TABLE 37.2 Nineteenth CenturyExplosive Discoveries

1800 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 PETN


choice as a propellant or bursting charge untilthe inventions of the late 1800s, when smokeless powder, based on nitrocellulose, provedto be a cleaner, safer, and more effective propellant than black powder. The synthesis ofpicric acid (2,4,6-trinitrophenol) followed byTNT and PETN gave solid, powerful, molecular explosives of more uniform performancefor use in bombs and artillery shells.The main explosives used in World War Iwere TNT, Tetryl (2,4,6-trinitrophenylmethylnitramine), and Hexyl (hexanitrodiphenylamine), and in World War II they wereTNT, PETN, and RDX (l,3,5-trinitro-l,3,5triazacyclohexane)."

In the industrial arena the production ofblack powder in the United States droppedprecipitously after reaching a peak of277 million lb in 1917.iSBy the mid-l 960s ithad ceased to be of commercial significance,but during the same time period dynamiteproduction rose from 300 million Ib to600 million lb.

In 1947 a spectacular accident ofcatastrophic proportions ushered in the nextrevolution in explosives. Fertilizer-grade AN,in the form of prills (small spherical particlescoated with paraffin to prevent caking), wasbeing loaded into ships in Galveston Bay,Texas. Along with other cargo, one of theseships, the partially loaded SS Grandcamp,contained 2300 tons of this material. On themorning of April 16, soon after loading wasresumed aboard the Grandcamp, a fire wasdiscovered in one of the holds containing AN.Efforts to extinguish the fire were unsuccessful, and an hour later the bulk of the coatedfertilizer detonated, killing 600 people andinjuring 3000.16

This tragedy, along with several other largescale accidents involving AN explosions,finally led researchers to the conclusion thatinexpensive, readily available, fertilizer-gradeAN could be used as the basis for modemindustrial explosives.

Soon after the advent of porous AN prills,introduced in the early 1950s, investigatorsrealized that these prills readily absorbed justthe right amount of Fa to produce an oxygenbalanced mixture that was both an inexpensive

and effective blasting agent, in addition tobeing safe and simple to manufacture. Thistechnology was widely adopted and soon constituted 85 percent of the industrial explosivesproduced in the United States. I? With ANFO'scost and safety characteristics, it becamepractical for surface miners to drill largerboreholes and to utilize bulk ANFO deliverysystems. Nevertheless ANFO had two significant limitations : AN is very water soluble, sowet boreholes readily deactivated the explosive; and ANFO's low density of 0.85 glcclimited its bulk explosive strength. COOkl8 hitupon the idea of dissolving the AN in a smallamount of hot water, mixing in fuels such asaluminum powder, sulfur, or charcoal, andadding a thickening agent to gel the mixtureand hold the slurried ingredients in 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 .Other oxidizers also could be added, and thedensity could be adjusted with chemicalfoaming agents to vary the bulk explosivestrength of the product. With the addition of across-linking agent, the slurry or water gelcould be converted to a semisolid materialhaving some water resistance. The latest significant development in industrial explosivesactually was invented only a few years afterslurries .19a

•b Water-in-oil emulsion explosives

involve essentially the same ingredients thatslurry composite explosives do, but in a different physical form. Emulsion explosives arediscussed fully under the section titled"Explosives Manufacture and Use."

The main developments in military types ofexplosives since World War II have beentrends toward the use of plastic bonded explosives (PBXs) and the development of insensitive high explosives. Driving these trends aredesires for increased safety and improvedeconomics in the process of replacing agingTNT-based munitions and bomb fills. PBXsinvolve the coating of fine particles of molecular explosives such as RDX and HMX(1,3,5,7-tetranitro-1 ,3,5,7-tetrazacyclooctane)with polymeric binders and then pressing theresultant powder under vacuum to give a solid


mass with the desired density. The final formor shape usually is obtained by machining.Explosives such as triaminotrinitrobenzene(TATB), nitroguanidine," and hexanitrostilbene (HNS)21 are of interest because of theirhigh levels of shock insensitivity and thermalstability. The synthesis of many new, potentially explosive compounds is a very activeand ongoing area of research,22,23 but recentlyinterest also has focused on composite explosives similar to those used by industry.Examples are EAK, a eutectic mixture of ethylenediamine dinitrate, AN, and potassiumnitrate," and nonaqueous hardened or castemulsion-based mixtures."

CLASSIFICATION OF EXPLOSIVES

The original classification of explosivesseparated them into two very general types:low and high, referring to the relative speedsof their chemical reactions and the relativepressures produced by these reactions. Thisclassification still is used but is oflimited utility because the only low explosives ofany significance are black powder and smokelesspowder. All other commercial and militaryexplosives are high explosives.

High explosives are classified further according to their sensitivity level or ease ofinitiation.Actually sensitivity is more of a continuumthan a series ofdiscrete levels, but it is convenient to speak ofprimary, secondary, and tertiaryhigh explosives. Primary explosives are themost sensitive, being readily initiated by heat,friction, impact, or spark. They are used only invery small quantities and usually in an initiatoras part of an explosive train involving less sensitive materials, such as in a blasting cap. Theyare very dangerous materials to handle andmust be manufactured with the utmost care,generally involving only remotely controlledoperations. Mercury fulminate, used in Nobel'sfirst blasting cap, is in this category, as is themore commonly used lead azide. On the otherend of the spectrum are the tertiary explosivesthat are so insensitive that they generally arenot considered explosive.

By far the largest grouping is secondaryexplosives, which includes all of the major

military and industrial explosives. They aremuch less easily brought to detonation thanprimary explosives and are less hazardous tomanufacture. Beyond that, however, generalizations are difficult because their sensitivityto initiation covers a very wide range .Generally, the military products tend to bemore sensitive and the industrial products lesssensitive , but all are potentially hazardous andshould be handled and stored as prescribed bylaw. Table 37.3 lists some of the more prominent explosives of each type, along with a fewof their properties.

For industrial applications, secondaryexplosives are subdivided according to theirinitiation sensitivity into two classes:Class 1.1 and Class 1.5. Class 1.1 explosivesare sensitive to initiation by a blasting capand usually are used in relatively small-diameter applications of 1-3-in. boreholes. Class1.5 (blasting agents) are high explosives thatare not initiated by a Standard # 8 electricblasting cap under test conditions defined bythe U.S. Department of Transportation(DOT), and that pass other defined testsdesigned to show that the explosive is "soinsensitive that there is very little probabilityof accidental initiation to explosion or of thetransition from deflagration to detonation.v"Being less sensitive, blasting agents are generally used in medium- and large-diameterboreholes and in bulk applications. Dynamitesare always Class 1.1, but other compositeexplosives made from mixtures of oxidizersand fuels can be made either Class 1.1 or 1.5,depending upon the formulation and the density. Density plays a significant role in theperformance of most explosives, and this isespecially true for slurry and emulsion explosives where the density may be adjusted byair incorporation, foaming agents , or physicalbulking agents, irrespective of the formulation. Blasting agent (class 1.5) classificationis of interest because regulations governingtransportation, use, and storage are less stringent for blasting agents than for Class 1.1explosives. (Propellants and fireworks areclassified by the DOT as Class 1.2 or 1.3explosives, and blasting caps and detonatingcord as Class 1.4.)

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STRUCTURAL CHARACTERISTICSOF EXPLOSIVES

The number of potentially explosive compounds is virtually unlimited. A listing by theU.S. Bureau ofAlcohol , Tobacco and Firearmsof explosive materials under federal regulation27 numbered 225, and many of the itemslisted were broad, general categories. The tenvolume Encyclopedia of Explosives andRelated Items compiled by the U.S. ArmyPicatinny Arsenal over a 25-year period contains several thousand entries. New organicmolecular explosives are being synthesizedcontinually; composite explosives, such ascurrent commercial products that are mixturesofoxidizers and fuels, present an infinite number of possible combinations. The complexityof trying to comprehensively list the chemicalstructures of explosives is shown by a 1977reference that listed 13 separate categories justfor primary explosives.f However, the majority of the most important explosives can begrouped into a few classes sharing commonstructural features that are of value toresearchers in understanding and predictingexplosi ve properties.

The following seven categories,29a,b updatedto include the relatively recent fluoroderi vatives," appear to be the most encompassing.Many explosives may contain more than onecategory, but not every compound that contains one of these chemical groups is necessarily an explosive.

l. -N=O2. - N- N-, -N= N-, and - N == N3. -C==N- and -C == N4. -C==C-5. -Cl=O6. -N-X, where X = Cl, F, I7. - 0-0-

Category I is by far the largest. It includesnitro groups, both aliphatic and aromatic;nitrate esters; nitrate salts ; nitramines; andnitrosamines. Nearly all of the explosiveslisted in Table 37.3 fall into this category.Prominent examples are: nitromethane, an

aliphatic nitro compound; TNT, an aromaticnitro compound; NG and PETN, nitrateesters; EDDN and ammonium nitrate, nitratesalts; and RDX and HMX, nitramines.Category 2 represents the hydrazine, azo,diazo , and azide compounds, both organicand inorganic. Hydrazine, tetrazene, and leadazide are examples of this group. Category 3is represented by the explosives mercury fulminate and cyanogen, respe ctively. Acetyleneand metallic acetyl ide salts constitute category 4. Category 5 consists mainly of inorganic and organic ammonium salts of chloricand perchloric acid, but would also includevarious chlorine oxides. Category 6 is generalized to include most of the amine halogens,nitrogen triiodide being a classic example.Also, considerable new synthetic work hasfocused on inserting the energetic difluoroamine groups into various organic molecules to form explosives that fall into thiscategory. Category 7 includes organic peroxides and ozonides as well as hydrogen peroxide itsel f.

Commercial industrial explo sives such asdynamites, slurries, and emulsions areincluded in these categories because theirmajor components, nitrate esters and nitrateand perchlorate salts, are listed. However,mixtures of fuels and oxygen or other gasesthat may be explo sive at certain ratios are notcovered, including the liquid oxygen explosives that saw limited application earlier inthe 20th century.

EXPLOSIVES MANUFACTURINGAND USE

Details of the synthesis and larger-scale production of a number of molecular explosivesincluding dynamites are given in the fourvolume series by Urbanski (Chemistry andTechnology of Explosives, Pergamon Press.1964-84) and in various military books suchas Engineering Design Handbook: ExplosiveSeries. Formulations of commercial slurriesand emulsions generally are cons ideredproprietary and are described mainly in thepatent literature. Some specific examples of


prominent explosives with general preparation methods are given below.

TNT 12,4,6-Trinitrotoluene)

TNT is no longer manufactured commercially in the United States, but is manufactured in significant quantities at severalgovernment plants because it is still animportant military explosive. It is producedcommercially in Canada and other countriesand is imported into the United States for usein cast boosters to initiate industrial blastingagents. In a relatively straightforward process,TNT is made by the direct trinitration oftoluene with nitric acid. Most modernprocesses are set up for continuous production in a series of nitrators and separatorswith the nitrating acid flowing countercurrently, This procedure avoids having to isolate the intermediate mono- and dinitrationproducts and may also employ continuouspurification and crystallization, being carriedout simultaneously with production.

Mixed nitric and sulfuric acids sometimesare used with the addition of S03 or oleum.The sulfuric acid or oleum helps drive thereaction to completion by removing the waterproduced by nitration and by dehydratingnitric acid to form the more reactive nitronium ion (NO~). Because toluene is not verysoluble in the acid, powerful agitation isrequired. The spent acid is removed in successive separation steps, and the sulfuric acid isreused after the addition of more nitric acid.The molten TNT product is purified with multiple water and sodium sulfate washes, whichproduce significant quantities of "yellowwater" and "red water" waste streams, respectively, that must be properly handled toavoid environmental problems. The lowmelting point of TNT (80-82°C) is ideal formelt casting, and TNT usually is employedas a mixture with other higher-meltingexplosives such as PETN, RDX, HMX, andtetryl. This feature and the excellent chemical stability of TNT have made it the mostpopular and widely used military explosivein the world.

RDX and HMX

Both RDX and HMX are cyclic nitraminesmade by nitrolysis of hexamethylenetetramine (HMT). Their good thermal stabilities, high melting points (>200°C), and highenergy properties make these crystalline compounds popular as projectile and bomb fillsand for use in cast boosters and flexible, sheetexplosives. HMX has superior detonationproperties and a higher melting point thanRDX but it is more difficult and more expensive to manufacture. Reaction I shows theformation of RDX by the action of nitric acidon HMT. Schematically, RDX formation canbe pictured as nitration of the three "outside"nitrogen atoms of HMT (in more accurate,three-dimensional representations all fournitrogens are equivalent) with removal of the"inside" nitrogen and methylene (-CH2- )

groups. AN (NH4N03) and formaldehyde(CH20) are produced as by-products but canbe used to form more RDX with the additionof acetic anhydride, as shown in Reaction 2.In actual practice these 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 impurityproduced in the RDX reaction. It is composed of an eight-membered ring rather thanthe six-membered ring of RDX. The latteris more readily formed than the eightmembered ring, but with adjustment of reaction conditions (lower temperature anddifferent ingredient ratios), HMX formationcan be favored. Schematically its formationcan be pictured by nitration of all four nitrogens in hexamethylene tetramine andremoval of two methylene groups as indicated in Reaction 3. To obtain pure HMXthe RDX "impurity" must be removed byalkaline hydrolysis or by differential solubility in acetone.

HNS 12,2',4,4',6,6' -Hexanitrostilbene)

This is a relatively new explosive having beenprepared unequivocally for the first time inthe early 1960s.30a,b It is of interest primarily


Reaction 1

HMT

Reaction 2

Formaldehyde AN Acetic anhydride

Combined Reaction

RDX Acetic acid

Reaction 3

for two reasons: (1) its high melting point(316°C) and excellent thermal stability, and(2) its unique crystal-habit-modifying effectson cast TNT. The former makes HNS usefulin certain military and space applicationsas well as in hot, very deep wells, and thesecond property is used to improve TNT castings. It can be manufactured continuouslyby oxidative coupling of TNT as shownbelow.

This relatively simple process from readilyavailable TNT and household bleach (5%NaOel solution) has been shown to involve aseries of intermediate steps that give HNS inonly low to moderate yields (30-45%) withmany by-products. Although it also involvesthe use of expensive organic solvents thatmust be recovered, this synthesis is used commercially.31,32 Studies to improve this processconstitute an active area of research.

NaOCI-----+CH,OH

THFo-is-c

TNT HNS


TATB (1,3,5-Triamino-2,4,6trinitrobenzenel

This highly symmetrical explosive moleculehas even higher thermal stability than HNS(greater than 400°C) and has become ofspecial interest in the last two decadesbecause of its extreme insensitivity.Pv' ?"Because its accidental initiation is highlyunlikely, TATB has been used in nuclear warheads and is being explored in plastic bondedsystems for a number of military and spaceapplications.i" Currently it is manufactured inlarge-scale batch processes that are littlechanged from its original synthesis over 100years ago. The two-step process involves trinitration of trichlorobenzene followed byamination to displace the chlorine groups asshown below.

~clMcl

NaNO,H2SO.

(SO,)----+

150'C4hr

product or to change its particle size byrecrystallization. Also the starting material isexpensive and not very readily available.

More recently a similar synthetic procedurestarting with 3,5-dichloranisole was reported."

DDNP (2-Diazo-4,6-dinitrophenoll

This yellow-to-brown crystalline material(melting point 188°C) is a primary explosiveused as the initiator charge in electric blastingcaps as an alternative to lead azide. It is lessstable than lead azide but much more stablethan lead styphnate, and is a stronger explosive than either of them because it does notcontain any metal atoms. DDNP is also characterized as not being subject to dead pressing(tested at pressures as high as 130,000 psi).It was the first diazo compound discovered(1858) and was commercially prepared in1928, It is manufactured in a single-step,batch process by diazotizing a slurry ofsodium picramate in water.

Trichlorobenzene

Trinitrotrichlorobenzene

The structure shown is convenient forvisualization purposes, but DDNP actuallyexists in several tautomeric forms with form(2) apparently predominating.

0

02NyYN=N

YN02

DDNP

NaND,-HCI

Sodium Picramate

CI NH 2

02N~N02 T~I~:n., 02N,-~N02

C1yCI ~:c H2NYNH 2

N02 N02

TATB

Both steps require high temperature andconsiderable reaction time but give 80-90percent yields. The major problem areas arechloride impurities in the final product andthe excessively fine particle size of the finalproduct. Because TATB is highly insolublein most solvents, it is difficult to purify the

0-

O'N'¢rN=N

N0 2

(I )

o,NhN",N

yN02

(2)


CH20HI

HOH 2C-C-CH20H +HCa(OOCHhJ

tH OH Calcium Formate2

Pentaerythritol

NG (Nitroglycerin or Glyercol Trinitratel

This nitrate ester is one of only a very fewliquid molecular explosives that are manufactured commercially. It is a clear, oily liquidthat freezes when pure at l3 0 C. As seen in thehistorical section, the first practical use ofNGwas in dynamites, where it is still used todaymore than 100 years later. It also is used as acomponent in multibased propellants and asa medicine to treat certain coronary ailments.This latter usage is attributed to NG'sability to be rapidly absorbed by skin contactor inhalation into the blood, where it acts as avasodilator. (At high exposure levels such asin dynamite manufacture and handling, thisproperty is responsible for the infamous powder headache.) NG is undoubtedly the mostsensitive explosive manufactured in relatively

solid alcohol added slowly with mixing andcooling. PETN is not very soluble in nitricacid or water and is readily filtered directlyfrom 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, crystalline solid witha melting point of 141.3°C. Because of itssymmetry it is said to have higher 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 of the most sensitive, noninitiating, military explosives." As with mostexplosives, the detonation velocity of PETNvaries with the bulk density of the explosive.Most military applications of PETN havebeen converted to RDX because of its greaterthermal stability. However, in industry PETNis widely used as the major component in castboosters for initiating blasting agents, as theexplosive core in detonating cord, and as thebase load in detonators and blasting caps. Forsafety in handling, PETN is shipped in clothbags immersed in water-alcohol mixtures anddried just before use.

Ca(OH),~

Ca(OH),~

FormaldehydeAcetaldehyde

The sodium picramate starting material isitself explosive, but is commercially availableas a chemical intermediate. It can be made bythe reduction of picric acid with reducingagents such as sodium sulfide. The key tomaking useful DDNP is to control the rate ofdiazotization so that relatively large, roundedcrystals are formed instead of needles orplatelets that do not flow or pack well.

For PETN manufacture the pentaerythritolstarting material can be readily purchased as acommodity chemical from commercial suppliers. The nitration is relatively simple,involving only nitric acid (96-98%) and the

PETN (Pentaerythritol Tetranitratel

Although known as an explosive since 1894,PETN was used very little until afterWorld War I when the ingredients to makethe starting material became commerciallyavailable. The symmetrical, solid alcoholstarting material, pentaerythritol, is madefrom acetaldehyde and formaldehyde, whichreact by aldol condensation under basiccatalysis followed by a crossed Cannizzarodisproportionation to produce the alcohol andformate salt. Although the reaction takes placein a single mixture, it is shown below in twosteps for clarity.


TABLE 37.4 General Types of Dynamitelarge quantities. Its sensitivity to initiation byshock, friction, and impact is very close tothat of primary explosives, and extreme safetyprecautions are taken during manufacture.Pure glycerin is nitrated in very concentratednitric and sulfuric acid mixtures (typically a40/60 ratio), separated from excess acid, andwashed with water, sodium carbonate solution, and water again until free from traces ofacid or base. Pure NG is stable below 50°C,but storage is not recommended. It is transported over short distances only as an emulsion in water or dissolved in an organicsolvent such as acetone. Traditionally it hasbeen made in large batch processes, but safetyimprovements have led to the use of severaltypes of continuous nitrators that minimizethe reaction times and quantities ofexplosivesinvolved. Because of its sensitivity, NG is utilized only when desensitized with other liquids or absorbent solids or compounded withnitrocellulose.

1. Straight dynamite

2. Ammonia dynamite("extra" dynamite)

3. Straight gelatindynamite

4. Ammonia gelatindynamite ("extra"gelatin)

5. Semigelatin dynamite

6. Permissible dynamite

Granular texture with NGas the major source ofenergy.

AN replacing part of theNG and sodium nitrateof the straightdynamite.

Small amount ofnitrocellulose added toproduce soft to toughrubbery gel.

AN replacing part ofthe NG and sodiumnitrate of the straightgelatin.

Combination of types 2 and4 with in-betweenproperties.

Ammonia dynamite orgelatin with added flameretardant.

Dynamite

Dynamite is not a single molecular compoundbut a mixture of explosive and nonexplosivematerials formulated in cylindrical paper orcardboard cartridges for a number of differentblasting applications. Originally Nobel simply absorbed NG into kieselguhr, an inertdiatomaceous material, but later he replacedthat with active ingredients-finely dividedfuels 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 mixing carefully weighed proportions of NG andvarious dopes to the desired consistency andthen loading preformed paper shells throughautomatic equipment. Because dynamitesrepresent the most sensitive commercial products produced today, stringent safety precautions such as the use of nonsparking andvery-little-metal equipment, good housekeeping practices, limited personnel exposure, andbarricaded separations between processingstations are necessary. Today, the "NG" usedin dynamite is actually a mixture of EGDN

and NG (formed by nitrating mixtures ofthe two alcohols), in which NG is 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.

Packaged Explosives

The use of NG-based dynamite continued todecline during the 1990's throughout theworld. For example, by 1995 there was onlyone dynamite manufacturing plant left inNorth America, and in 2000 the dynamiteproduction at this plant had dropped to lessthan half the amount produced in 1990. Thereasons for the declining use of dynamite areits unpopular properties of sensitivity to accidental initiation and the headache-causingfumes. Both bulk and packaged emulsionshave been slowly replacing dynamite sinceabout 1980.

Packaged emulsions are basically made withthe same manufacturing equipment as thebulk emulsions (see next section). The fuel

1758 KENT AND RIEGEL'S HANDBOOK OF INDUSTRIAL CHEMISTRY AND BIOTECHNOLOGY

Fig. 37.4. Commercial packaged emulsion cartridges.

component usually contains waxes and otherthickeners to give the emulsions a thick, puttylike consistency, and the oxidizer solutionoften contains both AN and a second oxidizersalt to produce optimum after-blast fumes.After manufacture, the thick emulsion isextruded into packaging material, normally aplastic film. The final product is then clippedtogether with metal clips forming firm,sausage-like chubs. Some packaged emulsionsare also available in paper cartridges, designedto simulate dynamite packaging. Figure 3704

shows some commercial packaged emulsioncartridges in both plastic and paper wrappings.

To obtain reliable detonability in smalldiameters, the density of packaged emulsionsmust be maintained at a relatively low value,typically 1.10-1.20 glee. On the other hand,some dynamites are available with densitiesin excess of lAO glee. These higher densityand energy dynamites have been the mostdifficult to replace with emulsions and arethe primary dynamite products currently inproduction.


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U 4500Ql

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~3500

5000

3000o 50 100 150 200 250 300

Diameter (rrm)

Fig. 37.5. Detonation velocity of ANFO versusdiameter and confinement.

efficient detonability of ANFO. The AN prillparticle density and inherent void-space valuealso become important when predicting andcalculating the densities ofANFO blends withwater-gel and emulsion explosives.

The bulk density ofANFO ranges from 0.80to 0.87 glcc. So, clearly about halfof the ANFOis air or void space. All explosives require a certain amount of entrained void space in order todetonate properly.These void spaces also playamajor role in the detonation reaction by creating "hot spots" under adiabatic compression inthe detonation front." The amount of voidspace in any given explosive and the resultantchange in density have a significant impact onthe detonation properties like detonation velocity, sensitivity, and even energy release.

Generally speaking, the detonation velocityof an explosive will increase with densityuntil a failure point is reached. This failurepoint is commonly referred to as the criticaldensity of that particular explosive. The density at that point is so high and the void spaceso low that the detonation cannot be sustainedand failure occurs .

Other important parameters that affect thedetonation velocity and performance ofANFO are charge diameter and confinement.The detonation velocity of ANFO willincrease by about 300 mls when the chargeconfinement is changed from a PVC tube to aSchedule 40 steel pipe. A summary of testdata on ANFO velocity versus confinementand diameter is shown in Fig. 37.5.

Ammonium Nitrate and ANFO

AN continues to be the most widely usedcomponent of commercial explosives. It isused in nearly all of the packaged and bulkexplosives on the market. The manufacturingprocess is described in Chapter 29.

Ammonia is basically the main raw materialneeded to manufacture AN. Some of the ANmanufacturers make their own ammonia andsome purchase it on the open market. It isobvious that the cost of manufacturing ANwill depend on the price of ammonia and,even more basically, natural gas from which itis made. The volatility of ammonia prices isshown by the fact that in 1992 it cost $95 perton and in 1995 the cost was $207 per ton."

There are many producers of AN in NorthAmerica making both AN solution and explosive grade AN prills. The AN solution is usedin the manufacture ofpackaged and bulk emulsion and water gel explosives, and explosivegrade AN prills are used to make ANFO.ANFO, the acronym for a mixture of AN andFO is the single most commonly used chemicalexplosive. (ANFO is an example of a composite explosive as described in an earlier section"Chemistry of Combustion and Explosions".)These low density AN prills are made by a specialized process, in which internal voids arecreated making the prills porous and able toabsorb the required 5.5-6 percent FO.

ANFO alone represents about three fourthsof the current volume of commercial explosives in use today around the world. Becauseof this, ANFO is commonly used as a reference when defining and comparing explosiveproperties. Some of these important explosiveproperties include density, detonation velocity,and energy release.

The crystal density ofAN is about 1.72 glcc,and the particle density of explosive-gradeAN prills ranges from lAO to 1045 gleedepending upon the manufacturing process.This difference in crystal and particle densityreveals the volume of pores or voids createdby the specialized prilling process . The porosity of AN prills is the property desired in themanufacture of ANFO, since this determineshow much FO can be absorbed. This intimatemixture of AN with FO is critical in the


The basic chemical reaction of ANFO canbe described with the following equation:

3NH4N03 + CHz~ COz + 7HzO + 3Nz + 880 cal/g

Using CHz to represent FO is generallyaccepted, but it really is an oversimplification,since it is a mixture ofhydrocarbons. The heatenergy release of 880 cal/g is the theoreticalmaximum value based upon the heats offormation of the reactants and products.Of course, all of the products of detonationare gases at the detonation temperature ofabout 2700oK.

The theoretical work energy that is releasedfrom an explosive reaction can be calculatedusing a variety of equations of state and computer programs." Explosive energy can alsobe measured by a variety of techniquesincluding underwater detonation of limitedsize charges with concurrent measurementsof the shock and bubble energies." Eachexplosive manufacturer has an energy measurement and equation of state that is used tocalculate and report their product properties.This often leads to confusion and controversywhen explosive consumers try to compareproduct lines when given only technical information sheets. Since theoretical calculationsmust of necessity be based on a number ofassumptions, the only valid comparisons aredone in the field with product testing anddetailed evaluation of results.

Bulk Emulsions

During the past decade the commercial use ofbulk emulsion explosives continued toincrease. Bulk emulsion products began tosignificantly replace packaged products inunderground mining and in quarry operations. Also, bulk emulsion and ANFO blendsbecame very popular in large volume open-pitmining operations. Emulsions are made bycombining an oxidizer solution and a fuelsolution using a high-shear mixing process.The oxidizer solution is normally 90-95 percent by weight of the emulsion. It containsAN, water, and sometimes a second oxidizer

salt, that is, sodium or calcium nitrate. Thesolution must be kept quite hot, since thewater is minimized for increased energy, andthe crystallization temperature is typically50-70°C. The fuel solution contains liquidorganic fuels, such as FO and/or mineral oils,and one or more emulsifiers. An emulsifier isa surface active chemical that has both polarand nonpolar ends of the molecule. In thehigh-shear manufacturing process, the oxidizer solution is broken up into smalldroplets, each of which is coated with a layerof fuel solution. The droplets in thismetastable water-in-oil emulsion are basicallyheld together with the emulsifier molecules,which migrate to the surface of the disperseddroplets. In today's explosives industry, muchof the research work is directed towardsdeveloping better and more efficient emulsifier molecules that will improve the storagelife and handling characteristics of the bulkand packaged emulsions. The emulsifiers currently used in commercial explosives rangefrom relatively simple fatty acid esters withmolecular weights of 300--400 to the morecomplex polymeric emulsifiers having molecular weights in excess of 2000.

Figure 37.6 shows a photomicrograph of anemulsion explosive at 400 power with the typical distribution ofthe fuel-coated oxidizer solution droplets (normally 1-5 urn in diameter).Figure 37.7 shows a bulk emulsion exiting aloading hose and displaying the soft ice creamlike texture typical of bulk emulsions. Theviscosities of bulk emulsions can range fromnearly as thin as 90 weight oil to as thick asmayonnaise, depending upon the applicationrequirements. Emulsion viscosity increaseswith product cooling, but most emulsionscontinue to remain stable at temperaturesbelow O°C, which is considerably below thecrystallization temperature of the oxidizersolution. The oxidizer solution droplets in theemulsion are therefore held in a supersaturated state. Over time, the surface layers created by the emulsifier molecules can bebroken, and the oxidizer solution droplets arefree to form crystals. At this point the emulsion begins to "break down" and lose some ofthe desirable properties. For this reason the

Fig. 37.6. Photomicrograph of a bulk emulsion.

Fig. 37.7. Bulk emulsion exiting a loading hose.


emulsion composition must be optimized fora particular application in terms of its productstability and usable storage life.

The intimate mixing of oxidizer and fuel inemulsions give these explosives much higherdetonation velocities when compared toANFO. For example, in 150 mm diameterPVC ANFO has a velocity of about4000 m/sec, and a sensitized emulsion wouldhave a velocity closer to 6000 m/sec at a density of 1.20-1.25 glcc. Also, the layer of oilsurrounding each oxidizer solution droplet protects the emulsion from extraneous water intrusion 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.This can be a very important factor in today'senvironmentally conscious mining and explosives industry.

Bulk emulsions are generally nondetonableper se and must be sensitized with some typeof density control medium to become usableblasting agents. That is, voids, creating "hotspots," are required to sustain the detonationfront. The two most commonly used densitycontrol methods are hollow solid microspheres or gas bubbles created by an in-situchemical reaction. Both glass and plastic hollow microspheres are commercially availableand used by explosives 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 underground mining. Much of this has been due tothe development of innovative loading equipment and techniques. One example of this isshown in Fig. 37.8 which shows a smallvolume pressure vessel that can be used fordevelopment and tunnel rounds utilizing horizontally drilled boreholes. The bulk emulsionblasting agent is pressurized inside the vesseland literally squeezed through the loadinghose into the boreholes . A continuous columnof explosives is assured by inserting the loading hose to the back of the hole and extracting

it as the product is loaded. Much more complex underground loading units are availablefor loading bulk emulsion into boreholesdrilled at any angle to the horizontal fromstraight up to straight down. The emulsionexplosives used in these specialized loadingunits were specifically designed for underground use over twenty years ago, and havebeen successfully used in underground mining operations around the world. The fuel andoxidizer contents are carefully balanced, andthis, combined with the excellent water resistance and detonation efficiency, results in thenear elimination of after-blast toxic fumes,such as CO, NO, and N02. The fume characteristics of this product have been shown to beconsiderably superior to either dynamite orANFO. For example, a series of tests in anunderground chamber in Sweden comparedthe after-blast fumes of this emulsion toANFO. The CO was reduced from II to lessthan 6 Llkg of explosive, and the NO plusN02 was reduced from about 7 to less than1 Llkg of explosive.f

Many open-pit quarries also use bulkemulsions for their blasting operations. As thesize of the quarry increases, the size of theexplosive loading trucks also must increase.Truck payloads can range from 5000 to30,0001b of product. Figure 37.9 shows anemulsion pumper truck in a quarry in southFlorida. These particular trucks, with a payload of about 20,000 lb, are speciallydesigned for a site-mixed system, in whicheach truck is an emulsion manufacturing unit.Combining nonexplosive raw materialsdirectly on the truck maximizes safety andminimizes requirement for explosive storage.This particular bulk emulsion is manufactured at a rate between 300 and 500 Ib/minand sensitized to the desired density with achemical gassing system as it is loaded intothe boreholes. Figure 37.10 shows a Floridablast in progress. Note the ejection of cardboard tubes from some holes. These tubesmust be used in most areas to keep the boreholes from collapsing in the layered, corallimestone formation.

Many of the large volume metal and coalmining operations around the world have both


Fig. 37.8. Underground pressure vessel loader for bulk emulsion. (Courtesy Dyno Nobel)

bulk emulsion and AN prills stored either onsite or nearby so that any combination ofthese two products can be used. Figure 37.11shows a typical explosive staging area in alarge open-pit coal mine in Wyoming. Theexplosive truck in the foreground has compartments on board for emulsion, AN prills,and FO, so any combination ofproducts ranging from straight emulsion to straight ANFOcan be loaded. The truck has a capacity ofabout 50,000 lb and can deliver product to theboreholes at up to a ton per minute. Eachborehole can contain as much as 5 tons ofexplosive, and some of the blast patterns cancontain as much as 10 million total pounds.

The emulsion!ANFO explosive blend selection to be used in any given mining applica-

tion depends upon many factors. Typically,ANFO is the least expensive product, but italso has the lowest density and no waterresistance. As emulsion is added to ANFO itbegins to fit into the interstitial voids betweenthe solid particles and coat the AN prillsincreasing the density, detonation velocity,and water resistance. The density increasesnearly linearly with percent emulsion fromabout 0.85 glcc with ANFO to about 1.32 g/ccwith a 50/50 blend. This range of emulsion!ANFO blends is commonly referred to asHeavy ANFO. As the density increases, theamount of explosive that can be loaded intoeach borehole increases, and either drillpatterns based on ANFO can be spread out orbetter blasting results can be obtained.

1764 KENTAND RIEGEL'S HANDBOOK OF INDUSTRIAL CHEMISTRY AND BIOTECHNOLOGY

Fig. 37.9. Bulk emulsion loading truck in a Florida quarry.

It is commonly accepted in the explosiveand mining industry that at least 40-50 percent emulsion is required to protect theHeavy ANFO blend from borehole waterintrusion. Pumped explosive blends with60-80 percent emulsion can even be usedwhen severe water conditions are encountered. These product s can be pumped througha loading hose, which can be lowered to thebottom of the borehole and displace the waterduring loading. Trucks similar to that shownin Fig. 37.9 can be used for these products .Most Heavy ANFO products are more simplymixed and loaded through an auger into thetop of boreholes. For Heavy ANFO products

the holes must be either dry or dewateredusmg pumps .

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, the majority ofwhich can generally be described as CH2

hydrocarbon chains. Therefore , a very simplified chemical reaction for a basic emulsion issimilar to that for ANFO shown above.

By adding 15 percent water to the ANFOreaction described earlier, the theoret ical heatenergy release is reduced from 880 to680 callg. The difference is the energy price


Fig. 37.10. Florida quarry blast in progress.

paid for using water and converting it to steamin the detonation reaction. The advantages anddisadvantages of using ANFO or emulsionsbegin to become clear. ANFO is easily mixedand is probably the least expensive form ofexplosive energy, but it has no water resistance and has a relatively low loading density.Emulsions are considerably more complicated to formulate and manufacture, butthey have excellent water resistance and moreflexibility in terms of density, velocity,and energy to match rock types and blastingapplications.

INITIATION SYSTEMS

The first reliable initiation system forcommercial explosives could probably betraced back to Alfred Nobel's invention of theblasting cap in 1864. This, combined withhis subsequent invention of dynamite aboutthree years later, basically started the modernera of blasting. In the century that followed,the initiation systems became more and

more sophisticated and safe. Short and longperiod delay electric blasting caps wereperfected and detonating cord was developed.Detonating cord is a flexible cord made of clothor plastic with a core load of high explosives,usually PETN. Strings or circuits of detonating cord could be used to initiate severalexplosive charges with only one blasting cap.

Prior to about 1950 most of the commercialexplosives in the market were reliably detonable with just 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 highdensity and high velocity dynamite was usedas the booster charge, and later TNT-basedcast boosters came into the market. These castboosters continue to be used today in nearlyall large mining operations. Cast TNT byitself is not reliably detonable with a blastingcap or detonating cord, and so 40-60 percent


Fig. 37.11. Typical bulk explosives staging area in a large open-pit mine.

PETN is normally added to the TNT melt andsubsequent cast. The combination ofTNT andPETN is called Pentolite. TNT has a meltingpoint of about 80°C, which makes it an excellent base explosive for casting into forms. Themilitary has used this concept for decades forfilling bomb casings. Once the TNT hasmelted, other material can be added togive the final cast explosive composition thedesired properties. In the case of Pentolite

cast boosters the added material is finelydivided PETN. Commercial cast boosters areavailable in a variety of sizes from about10-800 g as shown in Fig. 37.12.

This very brief history relates the development in the commercial explosives industryof an explosive loading and initiation systemthat emphasized safety. An entire pattern ofboreholes can now be loaded with an insensitive blasting agent primed with cast boosters


Fig. 37.12. Some commercial cast boosters.

on detonating cord down lines. The downlines can then later be tied to surface detonating cord line, and the entire blast initiatedwith just one blasting cap after the blast pattern has been completely cleared of personnel. Delay elements were also developed thatcould be placed between holes to control theborehole firing sequence for maximum blastmovement and rock fragmentation.

Non-Electric Initiation

In 1967 Per-Anders Persson of Nitro Nobel ABin Sweden (now part of Dyno Nobel Europe)invented a non-electric initiation system,designated Nonel" that has revolutionized thisaspect of the explosives Industry. The Nonelsystem consists of an extruded hollow plastictube that contains an internal coating ofa mixture of powdered molecular explosive and aluminum. The plastic tube is inserted into andattached to a specially designed detonator orblasting cap. The Nonel tubing can be initiated

by a number of starter devices, one of whichuses a shotgun shell primer. The explosive/aluminum mixture explodes down the inside ofthe tube at about 2000 rn/sec and initiates theblasting cap. The tubing is about 3 mm outsidediameter and 1 mm inside diameter, and theexplosive core load is only about 18 mg/m, noteven enough to rupture the tubing. The Nonelproduct is not susceptible to the hazard associated with electric blasting caps wherein premature initiation by extraneous electricsources can occur. Figure 37.13 is a photograph of both an electric blasting cap with thetwo electrical wires and a typical Nonel unitwith the plastic tubing.

The 1990s saw a large increase in the useof Nonel products around the world toreplace both electric blasting caps and detonating cord down lines. It has long beenknown that detonating cord down lines disrupt and partially react with blasting agentscausing some degree of energy loss. Also,the use of surface detonating cords to initiate

1768 KENT AND RIEGEL'S HANDBOOK OF INDUSTRIAL CHEMISTRY AND BIOTECHNOLOGY

Fig. 37.13. An electric blasting cap showing electrical wires, typical Nonel unit with plastic tubing.

blasts can lead to noise complaints. As aresult , long-lead Nonels were developed toreplace the detonating cord in boreholes. Asdelay elements were perfected for the Nonelblasting caps, their application and use greweven further and especially in undergroundmining where a large percentage of blastingcaps is used.

Detonator manufacturers are now perfectinginitiation systems using electronic blastingcaps containing programmable delay circuitryand remote initiation features. The manufacturing cost of these units is currently relatively high, but as the science progresses theseelectronic detonators will likely be a wave ofthe future.

PART II. ROCKET PROPELLANTS

A rocket is a device that uses the expulsion ofinternally generated gases as a source ofmotive power. The gases used for propellingthe rocket are generated by chemical reaction

of a fuel and an oxidizer. The force that actsagainst a rocket as gases are expelled is calledthrust. Because rockets carry their own fueland oxidizer and do not rely on air, the thrustfrom reaction (combustion) of the propellantchemicals will act in a vacuum. Thus, rockets,unlike internal combustion engines, are capable of providing power in space as well as inthe earth's atmosphere.

The use of rockets has been traced to13th century China, but it was not until thedevelopment of the liquid-fueled V-2 inGermany during World War II that a practicallong-range missile using rocket propulsionwas achieved. Work during 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 effort and the spectacularspace exploration studies that followed. Thelaunching into orbit of the Sputnik satellitefrom the Soviet Union in 1957 was the initial


Case

Nozzle

~

yExpansion

Throat Cone

Fig. 37.14. Schematic drawing of a simple rocket.

ExitPlane

event in a huge expansion of rocket development efforts in recent years. These developments have resulted in rockets used for threeprincipal applications:

• space exploration and satellite launching• strategic missiles• tactical missiles

Space exploration efforts have been verywell publicized in recent years. These effortshave included such notable developments, inaddition to Sputnik, as the launching ofmanned rockets (with the first astronautsYuri Gagarin in the Soviet Union and AlanShepard in the United Sates), the Apollomissions to the moon (with Neil Armstrong'smomentous first step), the Russian,American, and International space stations,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 great commercialand strategic importance, has been thelaunching of satellites for purposes of communication, mapping, and surveillance.Launch vehicles for the U.S. space programhave included the Atlas Agena, Delta, Juno,Saturn, Scout, Thor, and Titan rockets.

The space exploration efforts were paralleled in the United States and the SovietUnion by the development of rocket-powered missiles for strategic military use. SuchU.S. systems as the Air Force Minuteman,Peacekeeper, and Small ICBM and the Navysubmarine-launched Polaris and Trident arewidely deployed.

The use of missiles for tactical militaryapplications has also been an area of majordevelopment since World War II. Among thefirst such applications were the JATO(rocket assisted takeoff) units used to provide power to boost launching of airplanes.Tactical missiles have become an importantcomponent of weaponry and include U.S.rockets such as the Navy Sidewinder andStandard Missile, the Army Hawk andHellfire, and the Air Force Sparrow,AMRAAM, and Phoenix.

PRINCIPLES OF ROCKET PROPULSION

The flight of rockets is based on the thrustachieved by expelling gases from the aft endof the missile; this provides a forward impetus. A schematic diagram of a simple rocketis shown in Fig. 37.14. Combustion of the


propellant causes pressurization of the chamber by hot gases; the pressure from the gasesis counterbalanced by the strength of thechamber. At a narrow opening, the throat,gases are allowed to escape, providing thrust.If there were no expansion cones, and gaseswere expelled at the throat, the force, F, acting to propel the rocket would be:

F = AtPc

where At is the area of the throat and P, is thechamber pressure. When an expansion cone ispresent, a new term called the thrust coefficient, Cr, enters the equation:

F = AtPcCr

The value of Cr depends on the ratio of thechamber pressure to the pressure at the exitplane, and on the ratio of the throat area tothe exit plane area. The optimum performance of a rocket results when the pressure atthe exit plane, Pe, is equal to the pressure ofthe surrounding atmosphere (which is oneatmosphere for firings at sea level and zeroatmospheres in space).

Because thrust is dependent on motordesign and the rate of propellant combustion,it is not a convenient measure of propellanteffectiveness. A parameter that is used tocompare effectiveness is the specific impulse,Jsp, which is equivalent to the force divided bythe mass flow rate of the propellant:

Jsp=~= Jrwhere w is the weight flow rate of thepropellant, W is the total weight of the propellant, and t is the time. Because the impulse isdependent on a variety ofparameters, it is customary to use the standard specific impulse,J:,ps' which is the value of the specific impulsefor an ideal rocket motor fired at 1000 psi,exhausting to 14.7 psi, with no heat loss, andwith a nozzle of 15° half-angle. Frequently,measured or delivered impulse, Jspd valuesfrom motor firings will be converted to J:,ps forcomparison with previous firings and withexpectations. The ratio of delivered to predicted impulse is termed the efficiency. In

engineering units, specific impulse is given in(pounds-force * seconds)/pound-mass. A thorough yet succinct discussion of the physicsand thermodynamics of rocket propulsion isfound in Sutton.f

The prediction of rocket propellant specificimpulse, as well as impulse under otherconditions, may be reliably accomplished bycalculation using as input the chemical composition, the heat of formation, and the density of the component propellant chemicals.Not only impulse but also the composition ofexhaust species (and of species in the combustion chamber and the throat) may becalculated if the thermodynamic propertiesof the chemical species involved are knownor can be estimated. The present standardcomputer code for such calculations isthat described by Gordon and McBride. 44

Theoretical performance predictions usingsuch programs are widely used to guidepropellant formulation efforts and to predictrocket propellant performance; however, verification of actual performance is necessary.

TYPES OF PROPELLANTS

The two principal types of rocket propellantin general use are solid propellants and liquidpropellants. Solid propellants are chemicalcompositions that burn on exposed surfacesto produce gases for rocket power. Liquid propellants rely on pumping or pressurized flowof stored liquids to the combustion chamber.The choice between solid and liquid propellants for a specific application depends on avariety of considerations; to date, many of thestrategic missiles and most of the tacticalmissiles rely on solid propellants because ofthe lower cost of the rocket and the greaterstorability of the propellant. On the otherhand, large space vehicles and rockets firedfor maneuvering in space use liquid propellants, in part because of the ready controllability of liquid systems. Less widely used arehybrid rockets, which use solid fuel and liquidor gas-phase oxidizer. If a single chemicalcompound (e.g., nitromethane) containingboth oxidizing and reducing functions in thesame molecule is employed to power a rocket,


it is called a monopropellant. If two chemicalscombine to provide the propulsion, they forma bipropellant system.

SOLID PROPELLANTS

A solid propellant rocket motor is quitesimple in concept, although in practice a complete motor is more complex. As shown inFig. 37.15, the rocket propellant is containedwithin a case, which may be metal or areinforced high-performance composite.Frequently, the case is internally shielded by abonded layer of insulation. The insulation iscoated with a liner that bonds the propellant tothe insulation. The integrity of the propellantto-liner bond is of utmost importance; failureat this interface during a motor firing canresult in a sudden increase in the area ofpropellant surface exposed to combustion ,with potentially catastrophic results .

The bore or perforation of the propellantgrain is a major factor in determining the ballistic performance of a rocket. In the simplestinstance, the grain has no perforation, and theburning is restricted to the end of the grain;the resulting end-burning rockets have a relatively long burning duration with low thrust.More commonly, a perforation extendsthrough the grain (center-perforated) and mayhave a cylindrical , star, cross-shaped, wagonwheel, or other more complex profile. Theconfiguration of the grain is used to control

the burning behavior of the propellant; themore surface area there is exposed, the morerapidly propellant will be consumed, affectingperformance over time. The length of time arocket motor will bum is governed not onlyby the perforation geometry, but also by theweb thickne ss of the propellant (distancefrom perforation to liner), the burning rate ofthe particular rocket propellant, and the throatdiameter of the nozzle. The pressure-timecurve resulting from motor burning may beneutral (a single pressure is achieved andmaintained throughout the bum), progressive,or regressive . Progressive burning leads toacceleration, whereas regressive burninggives lower pressure as the firing progresses.Tactical solid propellant motors frequently aremanufactured with two types of propellant: arapid-burning boost propellant to provide initial acceleration and a slower-burning sustainpropellant to complete the desired flight profile. The trajectory of missiles as a function ofpropellant properties, grain configuration, andmissile design may be reliably predicted orsimulated by sophisticated computer calculations. A typical tactical solid propellant-basedmissile is shown in Fig. 37.16.

Single and Double-Base Propellants.Early solid rocket propellants were based onprocessing methods similar to that used in therubber industry, with propellants extruded intothe desired grain configuration. Propellants

Perforation (Bore)Case

Propellant Grain

Fig. 37.15. A solid propellant rocket motor.


Fig. 37.16. Solid propellant-based HAWK tactical missile.

that have been successfully manufactured bythis technique include nitrocellulose (singlebase) and nitrocellulose-nitratoester (doublebase) materials.* Double-base propellantscontain both nitrocellulose and NG as theprincipal components; additionally, chemicals

*Triple-base propellants have also been produced, having double-base composition plus nitroguanidine,added as a combustion coolant or as a ballistic modifier.

such as stabilizers, plasticizers, and burningrate modifiers may be added as appropriate.Other nitratoesters also may be in double-basesystems. Extruded propellants usually are limited to small grain diameters «<12 in.) bythe size of the equipment required for extrusion, or by the difficulties of solvent removal ifa solvent-based process is employed.

A processing advantage is achieved with thecastable double-base systems; a rocket chamber is filled with particulate nitrocellulose


TABLE 37.5 Properties of Oxidizers Used in Solid Propellants

Heat ofFormationMolecular Density, 1iH?at 298 K, gAtom

Material Formula Weight g/cm' cai/JOO g Oxygen/JOO g

AP NH4CI04 117.4 1.95 -60.21 3.404AN NzH403 80.0 1.725 -109.12 3.748NaN NaN03 85.0 2.26 -131.23 3.530KP KCI04 138.6 2.53 -74.49 2.887RDX C3H6N606 222.1 1.82 +6.61 2.701HMX C4HsNsOs 296.2 1.90 +6.05 2.701

(casting powder), which then is treated withNG-containing lacquers or a mixture of nitratoesters. The nitrocellulose is swollen by thenitratoester to give the final propellant, a toughmaterial with relatively low elasticity.

Double-base propellants may be formulatedto include fuels such as aluminum metal, oxidizers such as ammonium perchlorate (AP),or energetic materials such as the highenergy-density nitramines RDX or HMX. Theresulting compositions are termed compositemodified double-base (CMDB) propellants. Afurther modification, the addition of a polymer that is curable with a low molecularweight curing agent, allows formulation ofpropellants with much improved mechanicalproperties over the temperature range ofusage. Such propellants are termed elastomermodified composite double-base (EMCDB)propellants, and are currently among the mostenergetic and highest-performance propellantformulations.

Composite Propellants

In recent years, the great majority of solidrockets have utilized composite propellants.Most composite propellants are based on asolid oxidizer and a curable liquid polymericbinder. The binder also serves as fuel.Optionally, metallic fuels such as aluminum orboron may also be used." The propellant components are mixed together, and then thebinder is cured to give the tough, flexible, elastomeric (rubbery thermoset) solid propellantrequired for modern missile use. An excellentsource of information on the formulation ofsolid propellants is a report by Oberth."

Oxidizer. The major component, by weightand volume, of composite solid propellants isthe oxidizer. By far, the most important oxidizerused isAp,a crystalline solid material ground toexacting particle size distributions.This chemical possesses the desirable properties of highdensity, good thermal stability, and oxygenavailability, and relatively low reactivity andcost. Properties of AP and several othermaterials that are used as oxidizers are summarized in Table 37.5.

AN has been considered as an oxidizer formany applications; but its principal use to dateis in gas generator propellants, where generation of gases is required to provide initial motorpressurization or to power turbines.Widespread use ofAN has been hindered by apropensity of the compound to undergo numerous crystalline phase transitions, some involving a large (4%) volume change of the oxidizer,with concomitant oxidizer particle and binderdegradation, upon warming or cooling. Phasestabilized AN (PSAN), which avoids this difficulty, has been developed but for variousreasons has not yet found widespread use. Anarea of potential application for AN is insensitive minimum smoke propellants, which bettermeet military criteria of handling and storagesafety. Another alternative solid propellantoxygen source, sodium nitrate, has beendemonstrated as a cooxidizer-scavenger propellants. These propellants contain sufficientalkali metal (sodium) in the formulation toreact with the chlorine generated during combustion of the major oxidizer, AP. Sodiumchloride, rather than hydrochloric acid, is produced in the exhaust stream as the final chloride-containing reaction product. The benefit


of scavenging the chloride ion is loweredexhaust toxicity; however, a substantial loss ofpropellant impulse results.

The energetic nitramines, RDX and HMX,provide excellent impulse and nonsmokyexhaust, but their use gives propellants thatmay detonate when subjected to shock orimpact. The possibility of unwanted violentburning or detonation of propellants duringtransport or storage has resulted in recentemphasis on the development of insensitive(reduced hazard) rocket propellants for tactical applications. Special attention arerequired in using these energetic materials."

A number of other materials have receivedattention as potential oxidizers for propellantuse, but to date have found little actual use.They include hydroxylammonium nitrate(HAN), hydroxylammonium perchlorate(HAP), hydrazinium nitrate (HN), hydrazinium perchlorate (HP), and hexanitroisowurtzitane (CL-20).

Metallic Fuels. In rocket applications whereexhaust smoke is not a major concern, the use ofmetallic fuels adds considerable impulse to thecomposition. By far, the most common metal inuse as a solid propellant fuel is finely dividedaluminum, because of a combination of severaldesirable properties:

• low equivalent weight• high heat of formation of its oxide• low reactivity• relatively high density• low volatility• low cost• low exhaust product toxicity

An interesting comparison of some properties ofmetals with respect to their use as solidpropellant fuels is available.f

Although theoretical considerations indicate that boron and beryllium might be preferred to aluminum, practical considerationsdictate otherwise. Some of the theoreticaladvantage of boron is lost because of thevolatility of the oxide, and because boron isoxidized to a mixture of oxidation states, notcleanly to the trivalent oxide. The use ofberyllium is, in general, not possible today

because of the high toxicity of the metal andits exhaust products. Aluminum is preferredto magnesium because of its lower equivalentweight and reactivity; aluminum metal powder normally has a thin oxide coating thatdiminishes its reactivity until combustiontemperatures are reached.

Binder. The binder of a composite solidpropellant serves the dual function of providing a matrix to hold the oxidizer and the metalfuel, and of serving as a fuel itself-althoughits total makeup in modern formulations mayonly be 8-10 wt percent. The binder of the propellant usually is considered to consist of thepolymer, the curing agent, and the plasticizer-and can arguably include soluble stabilizers, as well.

In early years, natural rubber, asphalt,polysulfide-based organic polymers (Thiokolrubber), and acrylate polymers were employedas binders, but polymers based on polybutadiene, polypropylene, polyethylene, or polyesters have largely supplanted them. The twomost important types of prepolymers used inpresent propellants are those terminated withcure-reactive carboxyl or with hydroxyl functional groups. These functional groups are usedto react with curing agents (cross-linkers), asshown in Fig. 37.17, to provide the highmolecular weight polymer networks that function as propellant binders. In general, thelower molecular weight prepolymer introduced into the propellant formulation is di- orpolyfunctional so that the polymer resultingfrom reaction with a curing agent has a degreeof cross-linking sufficient to lend a desirabledegree of rigidity to the flexible propellant.The most common prepolymers in recent propellant use are the hydroxy-terminatedpolybutadienes; in the previous generation,carboxy-terminated polybutadienes wereemployed. For example, the binder used in thespace shuttle solid booster propellant is basedon PBAN, a carboxy-terminated terpolymer ofbutadiene, acrylic acid, and acrylonitrile.Hydroxy-terminated polyethers also are used,particularly in high-performance propellants.Hydroxy-terminated prepolymers, which arecured with linear or branched isocyanates to


Polyurethane Formatigno

Hydroxy-TerminatedPolymer

+ R'-NCO

Isocyanate Urethane

Acid-Epoxy Reaction

R-COOH

Carboxylic AcidTerminated Polymer

+o

R' CHZc~citz ~

Epoxide

o OH" ,

RCOCHZCHCHZR'

a-Hydroxy Ester

Acid-Aziridine Reaction

R-COOH

Carboxylic AcidTerminated Polymer

+

Aziridine

o 0II II

RCOCHZCHZNHCR'

Amide Ester

Fig . 37.17. Curing reactions used in present propellants. Each reactant is di- or polyfunctional , so thathigh molecular weight polymers are formed as the propellant binder.

give polyurethanes, offer advantages overcarboxylic acid-terminated prepolymers:

• lower mix viscosity• faster, lower temperature cure• lower susceptibility to side reactions• higher oxidizer and metal fuel solids

loading

New prepolymers based on 3,3-bis (azidomethyl)oxetane (BAMO) and 3-nitratomethyl- 3-methyloxetane (NMMO) are used in advanced pintlecontrollable solid rocket motor applications.These polymers yield favorable propellantenergy with the combination ofnitrato esters andammonium nitrate, and allow solid propellantdesigns to compete with liquid propellants inarenas of energy management, approaching truestart-stop-restart operation.

Plasticizer. In general, propellant formulations include plasticizers, which are nonreactive

liquid diluents used to improve processing andmechanical properties (particularly the low temperature properties) of the propellant. Plasticizerssuch as high-boiling esters (e.g., dioctyl adipate)or low molecular weight isobutene oligomers arefrequently used. In energetic formulations, nitratoester plasticizer blends, such as NG withBTTN, DEGDN, EGDN, and others, are used notonly to improve processing and low temperatureproperties but also to improve impulse and toserve as oxidizers. In such formulations, highplasticizer/polymer weight ratios (2- 3+) are frequently used. The nitratoester plasticizers are notmiscible with the butadiene-based polymers,hence use of telechelic hydroxy-prepolymersbased on ethylene-oxide or propylene-oxiderepeat units are required. Because of this, highsolids loadings much above 75-80 wt percent arenot practical. By comparison, propellants basedon (poly)butadiene prepolymers and their appropriate plasticizers can achieve solids loadings of


Fig. 37.18. The solid booster rockets for the space shuttle are one of the most widely publicizedapplications of solid rocket propellants.

90 wt percent or higher, while simultaneouslyretaining high mechanical integrity for over 20years' service life expectation, a wondrousachievement!

Other Propellant Chemicals. In addition tothe binder, oxidizer, and fuel, a solid propellantmay have a variety of other chemicals added(usually in small amounts) for specificpurposes.These include:

• aging stabilizers or sequestrants• processing aids• bonding agents• cross-linking agents• burning rate modifiers• signature-modifying agents• cure catalysts• cure catalyst scavengers• combustion stability enhancers

The final propellant composition is a resultof the interaction of a considerable number ofchemicals, each of which is important and isselected either for one characteristic or forseveral reasons. The ultimate purpose of theformulation is to give a propellant whoseproperties are reproducible from batch tobatch and from motor to motor, and areadequate for the intended use as shown, forexample, in Fig. 37.18.

Classification of Propellents Based onExhaust Properties. Based on the exhaustproperties, solid propellants can be classified assmoky, reduced smoke, minimum smoke, orminimum signature propellants. The descriptionof these categories are listed as follows:

Smoky. Propellants containing metals (suchas aluminum) give exhaust with particulate


matter (such as aluminum oxide) which isvisible in the exhaust stream as smoke. Solidexhaust products such as aluminum oxideare called primary smoke. Smoky propellants formulated to reduce hydrogen chloride(HeI) emissions to less than one percent ofthe exhaust gas mixture are termed cleanpropellants.

Reduced Smoke. Propellants without metalsor primary smoke, but containing oxidizers suchas AP which gives HCI gas as a principal combustion product, are called reduced smoke propellants. If HCI is exhausted in atmospheres ofhigh or moderate humidity, water droplets willcoalesce about the HCI molecules, resulting in avisible exhaust trail of what is called secondarysmoke. In atmospheres of low humidity, theexhaust plume of reduced smoke propellants isnot visible.

Minimum Smoke. Propellants with nometals, and having exhaust free of nucleatingspecies such as HCI, are termed minimumsmoke propellants.

Minimum Signature. Propellants whoseexhaust characteristics are tailored to give notonly minimum smoke properties, but also tohave low visible, ultraviolet, or infrared emissions are termed minimum signature propellants. Minimum signature propellants are ofinterest from the standpoints of launch site andmissile detectability and from considerations ofthrough-plume guidance.

Propellant Use Criteria. To functionproperly in its intended use, a propellant mustsatisfy a large number of criteria, as discussedin the following paragraphs.

Performance. The composition must haveadequate specific impulse and volumetricimpulse to perform its mission. Volumetricimpulse is the product of impulse and density(or density raised to a fractional power).

Mechanical Properties. The importantpropellant properties include the tensilestrength, strain capability (elongation), modulus

of elasticity, and strain endurance. The propellant is formulated so that it will be sufficientlyflexible to withstand the stresses of accelerationand temperature changes without cracking, yetbe sufficiently rigid so as not to slump or deformupon standing or undergoing temperaturechanges. Bonding agents, which improve theinteraction between polymer and filler (oxidizer), are frequently employed to improvemechanical properties.

Bond Properties. The strength of thepropellant-to-liner-to-insulation bond mustbe sufficient to maintain its integrity under thestresses mentioned above.

Ballistic Properties. Important parametersin this regard are the burning rate, the pressuredependence of the burning rate, and the temperature dependence of the burning rate. The burning rate is adjusted using the oxidizer particlesize and combustion-modifying additives asvariables. With AP oxidizer, finer oxidizer particles give faster burning rates. Finely dividediron oxide is a catalyst frequently employed toaccelerate the burning rate ofAP propellants. Ingeneral, low sensitivity of the burning rate tochanges in pressure or temperature is mandatory. Burning rates and ballistic properties aremeasured in progressively larger motor firingsas development of a propellant proceeds.

Combustion Stability. Although burningwithout acoustic oscillations is partly a motordesign concern, the propellant may be modifiedby the addition of refractory particles to dampensuch vibrations. If uncorrected, pressure oscillations from combustion instability may be largeenough to destroy a motor during firing.

Aging and Service Life. Propellants mustbe storable for at least as long as the intendedservice life of the missile system without undergoing degradation or change of ballistic ormechanical properties. Usually the service lifeis estimated by extrapolation from propertiesmeasured for sample aged at elevated temperatures. This accelerated aging is presumed tospeed processes that would take place at lower(storage) temperatures. Stabilizers selected to


enhance the aging capability are usual components of propellant compositions; the stabilizerchoice depends on the polymer, plasticizer, andoxidizer types.

Processibility and Castability. In order tobe introduced into a rocket motor, a castablepropellant composition must be blended until allcomponents are evenly dispersed. The resultingcomposition must be sufficiently fluid that itmay be cast into the motor without creatingvoids or bubbles in the propellant and yet be sufficiently viscous that dense particles (oxidizer,aluminum) do not settle, or less dense materials(polymer) rise to the surface. Certain chemicalscan significantly improve the processibility ofpropellants when added in small amounts.

Potlife and Cure. In addition to achievinga castable viscosity, it is necessary that theliquid (uncured) propellant remain fluid for asufficient amount of time to be transported,cast, and cleaned up, with allowance for possible delays, before it solidifies appreciably.Following cast, the composition must be curedto a solid, preferably at temperatures close tothe intended storage temperature. The balancing of potlife and cure rate frequently requirescareful adjustment of cure catalyst levels, catalyst scavengers, mix temperature, and curetemperature.

Hazard Properties. It must be verified thatthe propellant is sufficiently insensitive toshock, electrostatic discharge, friction, thermaldecomposition, or self-heating (in larger quantities) that it does not represent an unwarrantedhazard in its intended use. Rocket propellantsare energetic compositions and must be formulated so that chance stimulus will not initiateviolent reaction.

Ignitability. Conditions for ignition in thedesired application must be defined, andthe propellant formulated so that it may be reliably ignited under these conditions.

All of the above factors must be carefullystudied and optimized before a solid propellant can be considered adequate for itsintended use.

Composite Propellant Manufacture. In atypical batch processing sequence for a modem polyurethane-cure composite propellant, asubmix is prepared first. The submix containsthe liquid prepolymer, plasticizers, liquid orpowder-form stabilizers, and usually a(liquid) bonding agent; it is slurried withaluminum powder to give a premix. Thepremix is added to a moderate-shear slurrymixer, and AP oxidizer is added in severalportions with intervening mixing which mayinclude heating rate profiles and interim vacuum degas steps. Following addition of theoxidizer, the composition is mixed under highvacuum for a defined period. Vacuum isreleased, and the curing agent and curecatalyst(s) are added. After a final vacuummix, the propellant is ready for casting.Frequently, the propellant is cast into an evacuated motor; the use of vacuum increases thecasting rate and lessens the possibility of airentrapment and possible void formation inthe cured grain. The cast motor then is placedin a cure oven (typically held at a temperaturein the range of 11D-160°F) until the propellantslurry has cured to the desired hardness. Atmany points in the process, samples may betaken and analyzed to ensure motor qualityand integrity.

Although most solid propellants are manufactured in a vertical mixer batch process, acontinuous mixing process has been used successfully in the production of the first stageA-3 Polaris propellant and in the NASA 260inch demonstration motor program. The useof a continuous mixing process, in which propellant chemicals are metered into a helicalkneader, offers considerable benefit in termsof safety and cost for large-volume propellantproduction.

Liquid Propellants

Energetic materials which support rocketpropulsion via chemical and thermodynamicchanges in engines, as opposed to rocketmotors, distinguish the liquid propellant mission versus applications of solid propellants.Liquid propellants encompass liquid-phase


materials in the unreacted state, and are controlled by pressure- or pump-fed liquid rocketengine (LRE) components . Most commonly,liquid propellant rocket systems derive theirpropulsive energy from the combustion of aliquid fuel and a liquid oxidizer in a combustion chamber. Additionally, new liquid fuel oroxidizer blends, fuel and oxidizer gels, plussolid/liquid propellant hybrid systems are ofincreasing interest when combined withadvances in high strength, low weight, hightemperature materials, fast actuation components, or reduced toxicity requirements.

Liquid propellants can be categorized bytheir type of storage (cryogenic propellantsvs. storable propellants) or by their functionin the chemical propulsion system (oxidizers,fuels, bipropellants, or monopropellants). Incommon, is their physical state-usuallyliquid phase-from tankage to the injectorwithin the combustion chamber. In addition,selected liquid propellants, either oxidizer,fuel, or both may be gelled as a neat materialor as a heterogeneous gel mixture. Thesegelled propellants may contain suspendedsolid material such as metal fuel powder,together with polymeric or other particulategel additives, for rheology tailoring or performance enhancement, usually with militaryapplications in mind.

Chemical bipropellants include conventional fuel + oxidizer LRE designs that useeither cryogenic (less than - I50°C/ - 238°F)propellant fluids or storable fuels and oxidizers, the latter not requiring extensive facilitycooling or refrigeration launch support.Typical bipropellants include L02/LH 2 (cryogenic) or dinitrogen tetroxide/hydrazine (storable). Monopropellants may be classifiedseparately as either fuels or oxidizers. Theirdecomposition via heterogeneous catalysts(such as iridium on alumina support in thecase of hydrazine monopropellant , or silverplated catalyst screens for hydrogen peroxidedecomposition) either provides the propulsivethrust or functions as gas generators.

Gel propellants can be considered as a separate category ofliquid propellant technology.They provide a unique application of solidpropellant processing techniques and materi-

als to the liquid propellant LRE designs,which maximize on some ofthe advantages ofboth liquid and solid propellant systems. Gelpropellants are thixotropic (shear thinning)liquids by nature of various gelling additives,either polymeric in nature, or as high surfacearea powders, or both, and flow readily underpressure. A key requirement of gel bipropellants is rheology matching the viscosity vs.shear rate and flow dependencies of both thefuel and oxidizer gel, such that optimum combustion requirements are met over the entiretemperature range of operation-no easy feat.Of benefit in gel systems are their improvedsafety in handling, for spills of either gelledfuels or oxidizers are easily contained.Advanced applications in gel propellants utilize energetic, insensitive, nanoparticulategellants and fillers together with reduced toxicity fuel or oxidizer liquids. The applicationof these combined technologies expands thecapability and performance of many conventional currently deployed solid- and liquidpropellant military and civil applications.

Of current intense study is the category of"green", or environmentally benign, propellants-most notably liquid hydrocarbon fuelswith liquid/gaseous oxygen or highly concentrated hydrogen peroxide-in studies in thiscountry and abroad. The economic, environmental, and toxicological advantages aboundwhen considering long-term effects of manufacturing, transporting, storing, deploying, ordisposing highly toxic storable propellantsbased on hydrazine and nitric acid chemistry.Increased use of high performance "green"propellant alternatives can only benefit theefficient utilization of space, while at thesame time improving the quality of land,water, and air resources in the ever-shrinkingglobal community.

Applications. To date, the liquid propellant systems used in chemical propulsionrange from a small trajectory control thrusterwith only 0.2 lbf (0.89 N) thrust for orbitalstation-keeping to large booster rocketengines with over 1.0 million lbf (4.44 MN)thrust. Bipropellant propulsion systems arethe most extensively used type today for


(b)

(a)

Fig. 37.19. (a) Small thruster used in Milstar and (b) high thrust-to-weight liquid oxygen/keroseneengines for commercial launch vehicles. (Courtesy Aerojet Propulsion)

applications in main combustion chambersand gas generators as shown in Fig. 37.19.The monopropellant propulsion system iswidely used in low temperature gas generators and auxiliary rockets for trajectory ororbital adjustment.

A major difference between liquid propellants and solid propellants used in chemicalpropulsion systems is the ease of use or controllability. The solid propellants are cast as asolid propellant grain. The burning rate isdependent on the propellant formulation andthe configuration design of the solid propellant grain in addition to the chamber pressureand grain temperature. The combustionprocess is continuous, and a quench and reignition combustion process may be difficult.For the liquid bipropellant system, the liquidfuel and the liquid oxidizer are stored in separate tanks and fed separately to the combustion chamber. The propellants are fed eitherby means of pumps or by pressurization withan inert gas. A controller generally is used tocontrol the flow rate of the liquid propellantsin the system. Ignition and reignition com-

bustion generally is employed to fit the mission requirements and objectives.

Small-orifice injectors are used to atomizeand mix the liquid propellants in appropriateproportions. The propellants enter the thrustchamber through the injection manifold andburn inside the thrust chamber. A typical liquid bipropellant rocket engine is shown inFig. 37.20.

PhysicalProperties. General physical properties, including freezing point, normal boilingpoint, critical temperature, critical pressure, specific gravity, heat of formation, and heat ofvaporization, of some conventionalor promisingliquid propellants are listed in Table37.6. Of thetemperature-dependent physical properties, suchas heat capacity, thermal conductivity, viscosity,and specific gravity, only the specific gravity isincluded in Table37.6. Generally, cryogenic propellants are listed at their normal boiling point,whereas the storable propellants are evaluated at68°P (293 K). Detailed information on the physical properties of the liquid propellants can befound in Vander Wall et a1.49 To obtain a wide

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TABLE 37.6 Properties of Common Liquid Propellants

Heat ofFreezing Boiling Critical Critical Formation Heatof

Molecular Point Point Temp. Press. Specific (cal/mol e Vapor.Propellant Weight ( F) ( F) ( F) (psia) Gravity at 298.16 K) (BTUllb: NBP)

L02 32.0 -362 -297 - 182.0 730.6 1.14" -2,896 91.62F2 38.0 -365 -307 -201 808.5 1.50" -3,056 71.5NP4 92.011 11.75 70.4 316.8 1,441.3 1.45b -4.7 178.2CIFs 130.445 -153.4 7.3 289.4 771 1.795b -60,500 76.04H202 34.016 31.2 302.4 855 3,146 1.38b -44,750 76.04H2 2.016 -434.8 -423.3 -399.9 188 0.071" - 1,895 195.3Nll4 32.045 34.75 237.6 716 2,131 1.008b 12,054 583MMH 46.072 - 62.3 189.8 594 1,195 0.879b 13,106 377UDMH 60.099 - 70.94 144.18 482 867 0.785b 12,339 250.6A-50 4 1.802 22.0 158 633 1,731 0.905b 12,310 346.5(50% N2H c 50% UDMH)RP-I(H/C = 2.0) 172.0 - 55 422 758 340 0.807b -6,222 125Hp 18.016 32 212 705.4 3,206.2 1.0b - 68,317 970.3

"Evaluated at NBP; 'Evaluated at 68°F (293.4 K).

operating range and a large payload capacity, thedesired physical properties are:

• low freezing poi nt• low temp erature variability• low vapor pre ssure• high specific gravity• high heats of for mation and vaporization

Because liqu id propellants may also be usedto cool the thrust chamber assem bly, goodheat transfer properties, such as high hea t ofvaporiza tion, high thermal conductivity, highspeci fic heat, and high boiling poi nt , aredesirable.

Liquid Oxidizers. Liquid oxidizers can becategorized as either storable or cryogenic.Many different types of liquid oxidizers havebeen used in chemical propulsion systems. Ingeneral , cryogenics such as liquid oxygen, fluorine, or fluorinated compounds give a high specific impulse. Several storable oxidizers such asnitrogen tetroxide (N20 4) , inhibited red fumingnitric acid (IRFNA), or chlorine pentafluoride(ClFs) have been used for their advantages instorage . A brief description of the commonlyused oxidizers is given below.

Cryogenics. Liqu id oxygen, the mostimportant and extensively used liquid oxidizer,

is used primarily with liquid hydrogen to give avery high specific impulse (usually near or over400 lbf-sec/lbm ), Major applications of the liquid oxygen and liquid hydrogen bipropellantsystem include the space shuttle main engineand the Saturn second stage engine (1-2). Liquidoxygen is also widely used with hydrocarbonfuels in the booster engine of heavy lift launchvehicles such as the Russian Energia. Althoughliquid oxyge n can be used with storab le fuels,such as hydrazine or monomethylhydrazine(MMH), this bipropellant comb ination engine isstill in the development stage, mainly because ofthe difficulty of chamber cooling and combustion stabil ity.

Both the freezing point (- 362°F, 54.5 K)and the boiling point ( - 297°F, 90 K) ofl iquidoxygen are low, permitting a wide range ofoperation. Liquid oxygen is highly react ivewith most organ ic materials in a rap idly pressur ized confine ment region of rocket combustion cham bers. Except for the relatively highevapo ration rate, the handl ing and storageproblem s for liquid oxygen are min im al.Althoug h liquid oxygen is not conside red corrosive and toxic, the surfaces that wi ll be incontact with the liquid oxygen mu st be keptextremely free of any contamination becauseof its reactivity. The low boiling po int also cancause problems due to low temperature


embrittlement. In order to minimize oxidationproblems, metals such as copper are used.

Storage tanks and transfer lines of liquidoxygen systems must be well insulated to prevent the condensation of moisture or air withsubsequent ice formation on the outside.Vacuum jackets, formed plastics, and alternate layers of aluminum foil and glass-fibermats have been used successfully.

Liquid fluorine and fluorine compounds (F2,OF2, or NF3) are also cryogenic oxidizers.Although fluorine offers specific impulse anddensity advantages, extreme toxicity and corrosiveness have prevented the practicalapplication of fluorine and fluorinated compounds in chemical rocket design. In addition,with fluorine the handling problems are significant because fluorine has the highest electronegativity, hence reactivity, of any of theelements-plus a very low boiling point(85 K), necessitating extensive facility support requirements.

Storable. Nitrogen tetroxide and IRFNA arethe most important and most extensively usedstorable liquid oxidizers. A high density yellowbrown liquid, nitrogen tetroxide is very stable atroom temperature, existing as an equilibriumwith N02(N204f- f- 2N02), with the degree ofdissociation varying directly with temperatureand indirectly with pressure. At atmosphericpressure and room temperature N204 containsapproximately 15 wt. % N02, but at 303°F(423 K) it is essentially completely dissociatedinto nitrogen dioxide. Upon cooling, nitrogentetroxide dimer is re-formed. lt is used as the oxidizer for the Titan first and second stage 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.

The freezing temperature of nitrogen tetroxide (11. 75°F, 262 K) is relatively high, so caremust be taken to avoid freezing (causing flowblockage) whenever it is used. For this reason,nitric oxide (NO) may be added (applicationswith as much as 30 wt. % NO, as mixedoxides of nitrogen (MON), have been noted)to the nitrogen tetroxide to depress the freezing point, improving space-storability of this

oxidizer. Additionally, with 1-3 wt. % NO,storability in titanium tanks is greatlyimproved, due to reduced stress corrosionover time. Nitrogen tetroxide itself is not corrosive if pure, that is, if the moisture contentis very low. Carbon steels, aluminum, stainless steel, nickel, and Inconel can be usedwith it. However, when the moisture contentincreases above about 0.2 wt. %, the nitrogentetroxide becomes increasingly corrosive, and300-series stainless steel should be used.

IRFNA consists of concentrated nitric acid(HN03)that contains dissolved nitrogen dioxide and a small amount of fluoride ion, ashydrofluric acid (HF).

The addition of HF provides the fluorideion, which reacts with the metal containers,forming a metal fluoride coating and reducingthe corrosiveness significantly. As with nitrogen tetroxide, IRFNA is mainly used withhydrazine-type fuels in bipropellant systems.Because nitric acid ignites spontaneouslywith aniline and amines (hypergolicity), caremust be taken in handling and storing theIRFNA. However, this is an advantage in systems where extinguishment and reignition aredesired.

MON and high density acid (HDA) arevariants of storable oxidizers based on dinitrogen tetroxide. The MON propellants consist of N204 and NO, as noted earlier, andHDA is a mixture of nitric acid and N204.Both HDA and MON behave similarly toIRFNA.

Other liquid oxidizers, such as concentrated(usually >70 wt. %) hydrogen peroxide(H202), chlorine trifluoride (ClF3),and Clf', areused as rocket propellants for special applications. CIF3 and CIFs can be highly corrosive tometals. Other interhalogen compounds such asCI03F, CIF30, or BrFs can also be considered asalternatives. Rocket-grade hydrogen peroxide,recently available in quantity at concentrationsover 98 wt. % via the anthroquinone process, isgaining widespread respect as a "green" propellant option. However, hydrogen peroxide hasserious shortcomings in its incompatibility witha wide range of possible contaminants, whichhave resulted in catastrophic failure of lines andtanks in extended storage scenarios. Booster


Fig. 37.21. A 200-f (60-m) long flame shoots out from the Seal Aerospace second stage engine duringa test firing March 4, 2000. The engine is supposed to produce 810,0001b of vacuum thrust, usinghydrogen peroxide and kerosene propellants. (Photo courtesy of Beal Aerospace.)

applications have demonstrated, in static test firings, capabilities for high-performance heavylift launch vehicles using H20/kerosene propellants as shown in Fig. 37.21.

Liquid Fuels

Cryogenic. Liquid hydrogen, the most important 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 vaporization, high specific heat, and high thermalconductivity. It is a very good choice to cool thethrust chamber assembly when it is used in aregeneratively cooled system. However, the lowboiling point (-434.8°F, 14 K) and low densityof liquid hydrogen make it difficult to handleand store. The low fuel density means that avery large and bulky fuel tank is required; this isconsidered a disadvantage when a high ratio ofpayload to vehicle dry weight is desired. Liquidhydrogen has been found to react with metals,causing embrittlement of such metals as nickel.Copper is the best and most widely usedmaterial for liquid hydrogen in rocket engineapplications.

As with liquid oxygen , storage tanks andtransfer lines of liquid hydrogen systems mustbe well insulated, to prevent the evaporationof hydrogen or condensation of moisture or

air with subsequent ice formation on the outside . Vacuum jackets, formed plastics, orglass-fiber mats mixed with aluminum foilcan minimize the problems.

Molecular hydrogen exists in two forms:ortho-hydrogen (nuclei of the two atoms spinning in the same direction) and para-hydrogen(nuclei of the two atoms spinning in oppositedirections). These two forms are in equilibriumwith each other, and at room temperature theequilibrium mixture contains 75 percent of theortho form and 25 percent of the para form.Upon cooling to the normal boiling point(-425°F, 20.4 K), the equilibrium is shifted.At this temperature, the ortho form will convert slowly to the para form. The equilibriumconcentration ofpara-hydrogen at this temperature is 99.8 percent. (The shift of theortho-para equilibrium produces energy thatcauses a liquid hydrogen storage problem.)Therefore, para-hydrogen generally is used asliquid fuel for rocket engine appl ications.Modern liquefiers can produce liquid hydrogenthat is more than 99 percent para-hydrogen.50

Liqu id methane (CH4) , another kind ofcryogenic fuel used in testing and experiment,generally is used with liquid oxygen in abipropellant system. It has the advantage ofa considerably higher density than that ofhydrogen (the specific gravity for methane is0.4507 at (-258.7°F, 111.7k) the normal


boiling point). To date no operational rocketengine utilizes liquid methane as the fuel; allliquid oxygen/liquid methane engines are stillin the development stage.

Storable. Together with liquid hydrocarbons,hydrazine-type fuels are the most important storable liquid propellants. They include hydrazine(NzH4) , MMH, unsymmetrical dimethylhydrazine(UDMH), Aerozine-50 (50% NzH4 and 50%UDMH), and various blends of these fuels withother amine-based components. All hydrazinetype fuels are toxic to some degree, as are theirbreakdown products in the environment (especially, as in the case of diluteUDMH with nitratesand nitrites, forming carcinogenic and highlywater soluble nitrosodimethylamine, or NDMA).The most notable hydrocarbon storable fuelsinclude kerosene-based liquid propellants (RP-I,JP-8, and others).

A colorless liquid, hydrazine is stable toshock, heat, and cold. The freezing point ofhydrazine (34.75°F, 274.9 K) is the highestof commonly used hydrazine-type fuels.Because it starts to decompose at 320°F(433 K) with no catalysts present, it is undesirable for use as the coolant for regenerativecooling of the thrust chamber. Differentblends of hydrazine and MMH have beentested to improve heat transfer properties.Hydrazine is generally compatible with stainless steel, nickel, or aluminum. (See Chapter 22for more information on hydrazine.)

UDMH is neither shock- nor heat-sensitive,and it is a stable liquid even at high temperature. A key advantage is its low freezing point(-71°F). Furthermore, it is compatible withnickel, Monel, and stainless steel. UDMH isoften used as rocket propellant mixed withhydrazine in various proportions. A 50/50 mixture with hydrazine, Aerozine-50, is used forthe current Delta II Stage 2. Anecdotally, theTitan IV vehicle fly-out (last flight) occurred inOctober 2005 with vehicle B-26, a "black"mission with a satellite for the NationalReconnaissance office (NRO) engines.

MMH fuel is generally used with nitrogentetroxide (NZ04) oxidizer in small spacecraftrocket engines such as orbital maneuvering oraltitude control engines. Compared to

hydrazine, MMH has better shock resistanceand better heat transfer properties as acoolant. However, the specific impulse forMMH/Nz04 engines is slightly lower than thatfor hydrazine/Njo, bipropellant engines. Likehydrazine, MMH is compatible with stainlesssteel, nickel, aluminum, Teflon, and Kel-F.

In general, the hydrazine-type fuels do nothave very good heat transfer properties.Therefore, in the latest development of ahigh-pressure bipropellant system using NZ04

and hydrazine-type fuels, the oxidizer Nz04

has been used as a regenerative coolantinstead of the fuel itself.

Monopropellants. Simplicity and low costare the major reasons why monopropellantrocket engines are considered for developmentand deployment. The specific impulse formonopropellant engines generally is muchlower than that for bipropellant engines (inthe range of 200 lbf-sec/lbm for monopropellant vs. 280-400 lbf-sec/lbm for bipropellant). Hydrazine is the most important andwidely used monopropellant in small trajectory correction or altitude control rockets. Inan effort to lower the freezing point forimproved storability, many hydrazine blendshave been studied."

Hydrogen peroxide has been used as a monopropellant, especially in various-concentrationsolutions with water. It was used as a rocket propellant in the X-IS research aircraft. Current useof rocket-grade hydrogen peroxide, or "hightest" peroxide (HTP-generally greater than90% concentration in water) as a monopropellant is in the developmental stages, mostly forstation-keeping on orbit, or as an oxidizer-compatible pressurant gas source.5Z

,53 Long-termstorability ofhighly concentrated hydrogen peroxide is still problematic, although recentadvances in oriented crystalline polymers andother novel composites show great promise inlightweight yet compatible tankage materials.

Gelled Propellants. As with powderedmetallic fuels in solid composite propellants,early interest in gelled liquid propellantsfocused on gelation as a means of incorporating high-energy solids into liquid propellants


to achieve high specific impulse and density.Storable hydrazine-type fuels such ashydrazine and MMH have received most of theattention in gelation development. During thedevelopment ofTitan IIA*, a stable suspensionof aluminum powder in gelled hydrazine(called Alumazine) was developed and testedextensively. Later the needs for 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 of storable liquid propellantsrevived the interest in developing gelled liquid propellants. Although gelation technologyfor both cryogenic and storable liquid propellants has been developed, most of the activities have concentrated on storable propellants,especially in liquid fuels. Comprehensivereviews covering all gelled fuels developmentactivities can be found in references 54 and55. A brief description of the gelled fuels andoxidizers is given below.

Gelled Fuel. Gelled fuels generally haveconsisted 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 tacticalmissile applications. The gelled fuels withoutmetal additives have drawn added interest aspropellants with minimum or reduced exhaustsignatures and relatively high specific impulse.

Gelled fuels have essentially the same toxicities as their ungelled counterparts becausegelation does not significantly change theircompositions or equilibrium vapor pressure.However, the rates of vaporization aredecreased significantly, reducing the toxicexposure hazards. Gelled fuels, such asgelled MMH, are hypergolic but can burnonly upon direct contact of the fuel gel withoxidizer; the fire hazards are greatly reducedwith respect to both intensity and extent.Compatibility of the gelled fuels generally isthe same as those of the ungelled fuels as

*Titan I utilized kerosene and LOX as propellant; theTitan II ICBM development required earth-storablepropellant selection.

regards materials of tankage." There is evidence, however, that selected fillers or gelloadings in MMH have caused inordinate offgas and pressure increase over time withthese tactical fuel gels; ongoing studies areunderway to identify and minimize thispotential incompatibility in storage.

Gelled Oxidizers. Development work ongelledoxidizerswas startedduring the 1960s,butvirtually no effort was expended on them duringthe 1970s.Development work was revivedin the1980s as interest in gels was awakened becauseof their improved safety and handling characteristics. Gelled oxidizers include nitrogen tetroxide, MON, red fuming nitric acids (RFNA), andIRFNA.The gelling agents used for the oxidizersinclude powdered lithium nitrate (LiN03) ,

lithium fluoride (LiF), plastisol nitrocellulose(PNC), and colloidal silica. The early work onthese gels can be found in references 57 and 58.For tactical applications with minimum exhaustsignatures, gelled IRFNA and CIFs are the primary gel oxidizers.

Like the gelled fuels, the toxicity of gelledoxidizers is not reduced, but the handlingand safety hazards of storage are greatlyimproved. Gelled IRFNA is considered to becompatible with aluminum. Recent effortshave shown that it can be stored for at leastas long as the non-gelled IFRNA. Studiesat UAH in this country (sponsored by theU.S. Army Missile Command) and Universityof Nottingham (sponsored by the UnitedKingdom's Royal Ordnance) have identified mechanisms and additives to increasestorability of gelled IRFNA and analogs;their deployment, however, is yet to be seen.

ADVANCED MONOPROPELLANTSTUDIES

HAN, 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 these


propellants as both mono- and bi-propellants."As monopropellant, hydrazine has increasedcompetition from water-based ionic liquidblends that to a large degree include hydroxylammonium nitrate (HAN, NH 30HN03),ammonium dinitramide (ADN, NH4N(N02)2),

or ammonium nitrate (AN, NH4N03), and to alesser degree includes hydrazinium nitrate (HN,N2H5N03), hydrazinium nitroformate (HNF,N2H5C(N02)3), or perhaps hydrogen peroxide(HTP, H202).60-{;4 Blends of these compounds,with or without ionic or molecular fuels, havebeen studied for their applicability as gun propellants or monopropellants to varying degrees,without significant fielded deployments as ofthis date of writing. The predominant issuesthat prevent wider acceptance of these propellants include high combustion temperatures(on the order of 2000+ °C versus 1100°C forhydrazine), reliable performance with heterogeneous catalysts (typically iridium on aluminasupport), and their storability and compatibilitywith typical materials of construction.

In a series of gas-generating compositionsalso having utility as 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 The versatility of these blends offer not only reducedtoxicity as compared to hydrazine replacement monopropellants, but also as oxidizersin bipropellant or hybrid propulsion systems.Alternative applications may even includebreathable gas generation or use as an oxygensource for welding. These ternary blends areunique also in their low freezing points (as lowas - 50°C) and relatively high densities(1.3-1.6g/cc or greater) which make themattractive as improved performance optionsregardless of their reduced toxicity potential.However, as in the case for HTP or HAN useelsewhere, storage stabilities and potentialincompatibilities due to fume-off when inadvertently contaminated by decomposition catalystsmay make their use problematic. Work in government and industry labs is ongoing in theseareas in search ofrisk mitigation for use oftheseadvanced mono- and bipropellant materials.

BIPROPELLANT APPLICATIONS

The ongoing search for reduced toxicrtyand improved performance in both mono- andbipropellants is driven by cost factors andinfrastructure concerns as noted above, butalso in programs such as the U.S. nationaleffort Integrated High Payoff RocketPropulsion Technology (IHPRPT)69 multiphased goals. In our context of propellantsand their ingredients, the IHPRPT goals are todouble the performance of rocket propulsionsystems over the current state of the art, andto decrease the cost of access to space forboth commercial and military sectors.Predominant among the applications for thesehigh-payoff improvements in propellants, theboost and orbit transfer segment is a majorbeneficiary, with spacecraft and tactical (i.e.,defense) segments receiving a lesser benefit.

BIPROPELLANT FUELS

With many of the oxidizers discussed above interms of use as monopropellants, blends withionic and molecular fuels are noted to improvetheir performance, at the expense of hazardsratings or storage instabilities. Examples ofionic fuels intended for use as blends in monopropellants include tris(ethanol)ammoniumnitrate (TEAN), NH(C2H40HhN03, orhydroxyethylhydrazinium nitrate (HEHN),NH2NHCH2CH20H. Although these highenergy chemicals do show reduced toxicological activity in some studies," it would beconsidered premature to class many of thehydrazine-derivatized compounds as nontoxic.

The list of molecular fuels that can be combined with these emerging oxidants for use inmono- and bipropellant applications areextremely long-examples include urea,glycine, glycerol, methanol, ethanol, amines,organoazides, and more-but in general arehallmarked by their miscibility, gas-generatingpotential (high nitrogen content), and byimprovement to densities and standardenthalpies in their respective blends as fuelswith conventional or advanced oxidizers.Fundamental studies on combustion stability,hypergolicity, and associated ignition delay


Fig. 37.22. Nitrogen Tetroxide Liquid Oxidizer Handling Demonstration, circa 1960s. Note the large volume of evolved N02 vapor (this oxidizer is near the boiling point at room temperature), a hazard concernin exposures to personnel.

reactivity between fuel and oxidizer streams invarious injector and combustion chamberdesigns are underway in government and commerciallabs at this time.

IGNITION DELAY

Arguably the most significant performancedetractor to replacements of hydrazine-typefuels is the slower hypergolic reaction timeobserved for low-toxicity replacement fuelswith nitric acid oxidizers, resulting in "hardstart" pressure spike phenomenon on enginestartup that in some cases may be criticallydrastic. Recent studies71

,72 that reinvestigate theignition phenomenon between new fuels andoxidizers take advantage of improvements inhigh-speed digital photography and fastresponse data acquisition, analyzed by powerful standalone desktop computers commonlyavailable to investigators both in the UnitedStates and abroad, invariably show the fast,efficient ignition event between hydrazine andnitrogen tetroxide (or MMH-IRFNA using alow-temperature storable bipropellant example). As a benchmark, either using quickscreen techniques of drop-on-drop testing andframe-by-frame analysis of high-speed video(see Figures 37.23 to 37.24), or studies involvingthe pressure transients in liquid rocket engine

combustion chambers, most investigatorswould agree that conventional hydrazine-family fuels with nitric acid-type oxidizers willreact in 10 milliseconds or less, and in somecases are shown to be an order of magnitudeless under optimum conditions. University,industry, and government work involving identification of factors that affect ignition delay inamine fuels show 3° amines <2°, 1° amineswhen tested in drop-an-drop screening withliquid IRFNA.73

-77 Other trends are: higher

amine content shows shorter ignition delay, asdoes less steric hindrance at the amine nitrogen,higher amine basicity, and multiple tertiaryamine groups, shortens ignition delay. In aromatic amines, primary amine functionalitytends to show shorter ignition delay thansecondary/tertiary aminearomatics. Surprisingly,volatility of various amine compounds did notcontribute to hypergolicity, whereas factors suchas low temperature or low pressures have beenseen to detract from hypergolicity and increaseignition delays. Proprietary designs of chambersand injectorsfor bipropellantrocketengineshavealso been studied in recent years for optimumsfor characteristics of mix and ignition-whichmost often shows much reduced delays asopposed to drop-an-drop screening tests-suchthat competitiveadvantagemay be demonstratedfor low-cost and high-performance (and fastresponse) applications.

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Fig. 37.24. Modern drop-on-drop hypergol screening tests here show a sequence of high speed digitalphotos (-2 milliseconds between frames) with advanced low-toxicity liquid fuel falling into fuming nitricacid liquid oxidizer. When compared to similar tests with alkylhydrazine fuels, these are much more visibly dramatic, but here have about twice the ignition delay.

Ignition delay phenomena ofhypergolic propellants are complex and understanding isincomplete for not only the mechanisticaspects of conventional bipropellants, but alsoadvanced amine-type reduced toxicity fuels foruse with nitric acid-type oxidizers. Both liquidphase and gas-phase reactions play a part,along with physical effects ofmixing, localized

temperature, and pressures surrounding theimpinging streams, plus intermolecular effectsamong the interacting fuel-oxidizer combinations, in short, an almost overwhelming set ofphenomena that may contribute to significantlyaffect the ignition and sustained combustionphenomenon for advanced hydrazine-familyreplacement fuels.


REFERENCES

I. Sudweeks, W. B., "Chemical Explosives," Chapter 30, in Riegel s Handbook of Industrial Chemistry, 9th ed.,1.A. Kent (Ed.), Van Nostrand Reinhold, New York, 1992.

2. Institute of Makers of Explosives, Publication on the Commercial Explosives Industry.3. Kramer, Deborah, A., United States Geological Survey, Explosives Statistics and Information, Minerals Yearbook

2003.4. Ornellas, J. Phys. Chern., 72, 2390 (1968).5. Kaye, S. M., Encyclopedia of Explosives and Related Items, PATR 2700, Vol. 8, pp. 99-100, U.S. Army

Armament Research and Development Command, 1978.6. Engineering Design Handbook: Explosives Series, Army Material Command Pamphlet 706---177, AD 764, 340,

p. 12, distributed by NTIS, 1971, Jan.7. Fedoroff, B. T., and Sheffield, o.E., Encyclopedia ofExplosives and Related Items, PATR 2700, Vol. 2, p. B165,

Picatinny Arsenal, Dover, NJ, 1962.8. Butler, A. R., ChernTech, p. 202 (Apr. 1990).9. Van Gelder, A. P.,and Schlatter, H., History ofthe Explosives Industry in America, Arno Press, New York, 1972,

(reprint of 1927 edition).10. Marshall, A., Explosives, Vol. I, History and Manufacture, P. Blakiston's Son & Co., Philadelphia, PA, 1917.11. Gregory, C. E., Explosives for North American Engineers, Trans Tech Publications, Cleveland, OH, 1973.12. "Black Powder," Explosives and Pyrotechnics, 16 (7) (1983, July).13. Explosives and Rock Blasting, Atlas Powder Co., Dallas, TX, 1987.14. Johansson, C. H., and Persson, P. A., Detonics ofHigh Explosives, Academic Press, New York, 1970.15. Blasters Handbook, 16th ed., pp. 14 and 109, Du Pont, 1980.16. Kintz, G. M. et aI., Report of Investigations 4245, U.S. Dept. ofInterior, Bureau of Mines (1948, February).17. Chern. Mark. Rep., p. 6 (Sept. 19, 1983).18. Cook, M. A., The Science ofIndustrial Explosives, p. 2, IRECO Chemicals, Salt Lake City, UT, 1974.19. (a) Egly, R. S., and Neckar, A. E., U.S. Patent 3,161,551, Dec. 15, 1964.

(b) Bluhm, H. E, U.S. Patent 3,447,978, June 3, 1969.20. Bower,1. K., et aI., 1& EC Prod. Res. Develop., p. 326 (Sept. 1980).21. Mohan, V K., and Field, 1. E., Combust. Flame, 56, 269 (1984).22. Spear, R. 1., and Wilson, W. S.,J. Energ. Mater., 2, 61 (1984).23. Coburn, M. D., et aI., Ind. Eng. Chern. Prod. Res. Dev., 25, 68 (1986).24. Dobratz, B. M., LA-9732-H, VC-45, Los Alamos National Laboratory, Los Alamos, NM (May 1983).25. Cranney, D. H., and Hales, R. H., Proceedings of the Fourteenth Symposium on Explosives and Pyrotechnics,

Franklin Research Center, 1990, Feb.26. Code of Federal Regulations, Title 49 Transportation, Part 173.114a, p. 272, Oct. 1, 1979 Revision.27. Federal Register, 55 (9), 1306 (Jan. 12, 1990).28. Tarver, C. M. et aI., "Structure/Property Correlations in Primary Explosives," Final Report, 76-2, Stanford

Research Institute, Menlo Park, CA (Feb. 4, 1977).29. (a) Brunswig, H., Explosivstoffe, p. 17, Barth, Braunschweig, 1909.

(b) Plets, V, Zh. Obshch. Khim, 5,173 (1953).30. Shipp, K. G., J. Org. Chern., 29, 2620 (1964).

(b) U.S. Patent 3,505,413, April 7, 1970.31. Kayser, E. G., J. Energ. Mater., 1, 325 (1983).32. Gallo, A. E., and Tench, N., J. Hazard. Mater., 9, 5 (1984).33. Delistraty, 1., and Brandt, H., Propell., Explos., Pyrotech., 7, 113 (1982).34. (a) Rizzo, H. E, et aI., Propell. Explos., 6, 27 (1981).

(b) Kolb, 1. R., and Rizzo, H. E, Propell. Explos., 4,10 (1979).35. Ott, D. G., and Benziger, T. M., J. Energ. Mater., 5, 343 (1987).36. Urbanski, T., Chemistry and Technology ofExplosives, Vol. II, p. 181, Pergamon Press, New York, 1965.37. Military Explosives, Department of the Army Technical Manual TM 9-1300-214, pp. 7-32, Washington, DC,

1967.38. The Sheet 22/00-November 8, 2000, Blue Johnson and Associates, Inc.39. Cook, M. A., The Science of High Explosives, pp. 178-183, American Chemical Society Monograph Series

No. 139, 1958.40. Ibid., Appendix II.41. Cole, R. H., Underwater Explosions, Princeton University Press, Princeton, NJ, 1948.42. Hanto, K., Internal Report on Fumes from Emulsion and ANFO, Dyno Nobel Europe, 1998.43. Sutton, G. P., and Biblarz, 0., Rocket Propulsion Elements, 7th ed., John Wiley & Sons, Inc., New York,

2001.


44. Gordon, S., and McBride, B. 1., Computer Program for Calculation of Complex Chemical EquilibriumCompositions. Rocket Performance, Incident and Reflected Shocks, and Chapman-Jouget Detonations, NASASP-273, Interim Revision, NASA Lewis Research Center, (March 1981).

45. Kuo, K. K., and Pein, R., "Combustion of Boron-Based Solid Propellants and Solid Fuels," Begell House,ISBN 084939919X, 1993, Jan.

46. Oberth, A. E., Principles of Solid Propellant Development, CPIA Publication 469, Chemical PropulsionInformation Agency, Baltimore, MD, 1987.

47. D'Andrea, B., and Lillo, E, "Industrial Constraints for Developing Solid Propellants with Energetic Materials,"J. Propul. Power, 15 (5), 713-718, 1999.

48. Dekker, A. 0., "Solid Propellants," J. Chern. Ed., 37, 597.49. Cadwallader, A., Liquid Propellant Manual, Chemical Propulsion Information Agency, 1969.50. Von Doehern, 1., Propellant Handbook, AFRPL-TR-66-4, Air Force Rocket Propulsion Laboratory, 1966.51. Schmidt, E. w., Hydrazine and Its Derivatives, 2nd Ed., Vols. I and II, Wiley-Interscience, New York, 200 I.52. Wernimont, E. 1., and Mullens, P., (General Kinetics, Aliso Viejo, CA), Recent Developments in Hydrogen

Peroxide Monopropellant Devices, AIAAlASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 35th,Los Angeles, CA, 1999, June 20-24.

53. Murphy, T. H., Coffman, P. E., Jensen, 1.1., and Hoffman, C. S. (Boeing Co., Canoga Park, CA), Storable LiquidPropellant Usage-Trends in Non-toxic Propulsion, IAF, International Astronautical Congress, 49th, Melbourne,Australia, 1998, Sep. 28-0ct. 2.

54. Vander Wall, E. M., Andersen, R. E., and Cabeal, 1.A., "Preparation and Characterization of Gelled HydrazineBased Fuels Containing Aluminum," Final Report, AFRPL-TR-80-40, Air Force Rocket Propellant Laboratory(1980, July).

55. Haun, D. v., Ryder, D. D., and Graham, P. H., "Gelled Bipropellants for Advanced Missile Propulsion Systems,I. Fuel Component Initial Characterization," CPIA Publication 425, Vol. VI, pp. 215-224, JANNAF PropulsionMeeting, 1985, April.

56. Thompson, D. M., U.S. Patent 6,210,504; Azidoalkyl-substituted Tertiary Amines as Fuel Components forLiquid- or Gel-based Rocket Propellants, Assigned 1999.

57. Vander Wall, E. M., Anderson, R. E., Beegle, R. L., Jr., and Cabeal, 1.A., "Gelation ofNz04 and MON-25," FinalReport, AFRPL-TR-82-49, Air Force Rocket Propulsion Laboratory (Aug. 1982).

58. Allan, B. D., "A Gelled Oxidizer for Tactical Missiles," CPIA Publication 370, Vol. V, pp. 11-20, JANNAFPropulsion Meeting, 1983, Feb.

59. Edwards, T., "Liquid Fuels and Propellants for Aerospace Propulsion: 1903-2003," J. Propul. Power, 19 (6,Nov-Dec), 2003.

60. Schmidt, E. W., and Wucherer, E. J., "Hydrazine(s) vs. nontoxic propellants-Where do we stand now?, inProceedings of the 2nd International Conference on Green Propellants for Space Propulsion, June, 2004 (ESASP-557).

61. Wingborg, N., Larsson, A., Elfsberg, M., and Appelgren, P., "Characterization and ignition of ADN-based liquidmonopropellants," in 41st A1AA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Tucson, AZ July2005 (AIAA 2005-4468).

62. Amariei, D., Courtheoux, L., Rossignol, S., Batonneau, Y., Kappenstein, C., Ford, M., and Pillet, N., "Influenceof the fuel on the thermal and catalytic decompositions of ionic liquid monopropellants," in 41stAIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Tucson, AZ July 2005 (AIAA 2005-3980).

63. Slettenhaar, B., Zevenbergen, 1. E, Pasman, H. 1., Maree, A. G. M., and Moerel, 1. L. P. A., "Study on catalyticignition of HNF-based non-toxic monopropellants," in 39th A1AA/ASME/SAE/ASEE Joint PropulsionConference and Exhibit, Huntsville, AL, July 2003 (AlAA 2003-4920).

64. Bombelli, v., Maree, T., and Caramelli, E, "Non-toxic liquid propellant selection method-A requirementoriented approach," in 41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Tucson, AZ July2005 (AIAA 2005-4453).

65. Wagaman, K. L., U.S. Patent 6,165,295, Gas-generating Liquid Compositions (PERSOL 1), Dec 2000.66. Wagaman, K. L., U.S. Patent 6,331,220, Gas Generating Liquid Compositions (PERSOL 2), Dec 2001.67. Wagaman, K. L., U.S. Patent 6,299,711, Gas Generating Liquid Compositions (OXSOL 3), Oct 2001.68. Wagaman, K. L., U.S. Patent 6,328,831, Gas-generating Liquid Compositions (Perhan), Dec 200 I.69. Integrated High Payoff Rocket Propulsion Technology (IHPRPT) Program, http://www.pr.afrl.af.mil/projects.htm.

Aug 2005.70. Trohalaki, S., Zellmer, R. 1., Pachter, R., Hussain, S. M., and Frazier, 1. M., "Risk assessment of high-energy

chemicals by in vitro toxicity screening and quantitative structure-activity relationships," Toxicol. Sci. 68,498-507 (2002).

71. Pourpoint, T., and Anderson, W. E., "Physical and chemical processes controlling fuel droplet ignition," in 40thAIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Fort Lauderdale, FL, July 2004 (AIAA 20044009).


72. Pourpoint, T., and Anderson, W. E., "Environmental effects on hypergolic ignition, in 41stA1AA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Tucson, AZ July 2005 (AIAA 2005-3581).

73. Durgapal, U. c, Dutta, P. K., Pant, G. c, Ingalgaonkar, M. B., Oka, V. Y., and Umap, B. B., "Studies on hypergolicity of several liquid fuels with fuming nitric acids as oxidizers, Propel!. Explos., Pyrotech. 12, 149-153(1987).

74. Rapp, L. R., and Strier, M. P., "Chemical aspects ofhypergolic ignition for liquid propellant rocket engines," inAmerican Rocket Society Fall Meeting, Buffalo, NY, September 1956 (ARS paper 331-56).

75. Phillips Petroleum Company, Petroleum Derivable Nitrogen Compounds as Liquid Rocket Fuels, Final Report,USAF Contract AF 33(616)-2675, November 15, 1956 (DTIC ADI28399).

76. Saad, M. A. et aI., Ignition of Hypergolic Liquid Propellants at Low Pressure, Final Report, Contract AFAFOSR-73-2498, March 1974 (NTIS AD-778964).

77. Perlee, H. E., and Christos, T., Summary of Literature Survey of Hypergolic Ignition Spike Phenomena, Phase IFinal Report, United States Department of the Interior Bureau of Mines, Pittsburgh, Pennsylvania, April 8 toDecember 31, 1965.

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