•

TECHN ICAL REPORT ARB RL-TR-02308 v'

THE. INFLUENCE OF PHYSICAL PROPERTIES

ON BLACK POWDER COMBUSTION

OTIC

SELECTE"JUN 161981U

B

March 1981

Ronald A. Sasse'

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US ARMY ARMAMENT RESEARCH AND DEVELOPMENT COMMANDBALLISTIC RESEARCH LABORATORY

ABERDEEN PROVING GROUND, MARYLAND'-- --------------_.-.1, .

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Additional copies of this report may be obtainedfro. the National Technical Inforaation Service.U.S. Departaent of Cam.erce, Sprinlfield, Viralnia221~1.

The findin'5 in this report are not to be construed asan official Department of the Army position, unless'so desilftated by other authorized docuaents.

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T. IIIE~OIllT NU"IEIII AhOVT ACCltUION NO I. III'lCI~lltNT'1 ':ATAI.OG NU....".

TECIINICAL REPORT ARBRL-TR~02308 -Aino.::Jr- 734. TtTI.E ("d .sub'III.) I. TY~1t 0,. IIIE~Oln • ~.IIIIOD CO"IIIIIDTilE INFLUENCE OF PIIYSICAL PROPr:RTl HS ON BRL Technical HeportBLACK POWDER COMBUSTION

•• PEIII"OIll..tHG 011I0. IIIE~OIllT HU...1t1ll

.-7. AU THOllle.) •. CONTIIIACT 011I OIllANT HUM.EIII(.)

Ronald A. Sasse' I'J~~fIR~"I~~1l~1'f1?~nz~«.~~'bN~~lA~DI'8U~nfpment Command

10. PIIIOGIIIAM EL.EMENT. PIIIOJECT. TASI<AIIIEA. WOIIII< UNIT NUMIEIIIS

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'.. IUPPI.EMENTAIIIY NOTEI

It. KEY WORDS (Contlnu. on , ...., •• • 'd. It n.c....". ..d 'd.n"'y Ily "'ocll nUlllller)

Blad powdl'rPropell an tPhysi.:al properties of hlack powder

20. A_Tl'lACT rc-e..... -,.-- .... It,,__..,~ 1"-V/1'1 by b'ocll n.....) lC 1t JIt has heen ob~ervcd that b Inc!< powder made from ingredients of the same 10

and fabricated 1I s i n~ the same manufacturing pro~edure resul ts in material exhibit ing J i fforent burning rateg, The current study was undertaken to determine ifthe physical properties of h1ad\. powder affected burning rate and establi~h ift Ill: so proporti«.'s varied from one proJuction batch to another.

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20. ABSTRACT: (Continued)

Physical properties of black powder were measured including surface area,pore si~e distribution, and internal free volume. Black powder derived from oakand maple charcoals was compared, and the effects of processing the material hya jet mill or ball mill were contrasted. Scanning electron microscopy revealedthat applied pressure, a manufacturing step used in making black powder, inducedconsiderable plastic flow that resulte~ in a fused conglomerate, cohesive masscontaining interconnecting passageways of about 0.1 micron diameter. Density,free volume, and surface area were found to be functions of burning ~ate. Basedon thcge relationships, the conclusion was offered that the degree of openness 01a grain of black powder is a significant factor affecting its burning rate. •

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TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS .

1. INTRODUCTION . .5

7

11. EXPERIMENTAL • • • • • . ••• 12

A. Black Powder Samples • • • 12

B. Scanning Electron Microscopy of Black Powder andCharcoal ..•.......• • . . . . . 1S

C. Comprcssion of SUlfur" Potassium Nitrate and Charcoal. 15

D. Mercury Intrusion Porl.>simctry . . 16

E. B.E.T. Surface Area Measurements 17

F. Density Measurements 17

VI. SUMMARY. . ..

!I

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III.

IV.

V.

RESULTS . • • . • • • • • • . . • • •

A. Black Powder and Charcoal S.E.M. Microphotographs .

B. Compression of Sulfur, Potassium Nitrate, and Charcoal.

C. Mercury Intrusion F'orosimetry • • •

O. B.E.T. Surface Area Measurements ••.

E. Density Measurements

DISCUSSION . . . . . • . • • • . •

A. Black Powder and Charcoal S.E.~. Measurements .....

B. Compression of Sulfur, Potassium Nitrate and Charcoal.

C. Mcrcury Intrusion Porosimetry •••••

O. B.E.T. Surfacc Area Measurements

E. Density Measurements

FUTURE PLANS

ACKNOWLEDGEMENTS

lU\FERENCES

APPENDIX

DISTRIBUTION LIST

17

17

18

28

28

33

33

33

35

38

40

44

47

49

49

51

55

59

Figure

LIST OF ILLUSTRATIONS

Page

1. Comparison of burning rates as measured by flame spread,o (ref. 16); closed bomb, C (ref. 14); and open airflamt. spread, A (ref. 13) . • • • • • 14

2. Black Powder, Lot 1 · · · · · · · · · · • · 19..3. Black Powder, Lot 6 · · · · · · · · • · · · · · · · · 20

4. Black Powder, Lot 10 · · · · · · · · · · · · 21

5. Bbck Powder, Lot 11 · · · · • · · · · 22

6. Oak nnd Maple Charcoals · · · · · · · 23

7. Oak and Maple Charcoals · · • • • · · · · · · · · 24

8. Oak Charcoal Extracted from Lot 1 · · · · · · · · • · · · 25

Y. Maple Charcoal Extracted from Lot 11 • • • · · · 26

, 10. Effect of pressure on potassium nitrate, su 1fur, andcharcoal · · · · · · · · · • · · · · · 27

11. Volume of mercury ent.ering three samples of black powder-Lot U . . · · · · . · · · · · · · · · · · · • · · · · · · 29

12. Volume of mercury entering three samples of black powder-Lot 10 . · · · · . · · · · · · · · · · · · · · 30

· . . . . . . . . .

Volume of mercury entering whole grains of black powder:A-lot 11, burn rate U.oO m/scc; .-lot 10, burn rate 0.51m/sec; • -lot 1, burn rate 0.32 m/sec; and 'Y -lot 6, burnra teO. 38 m/ sec • • • • III • • • • • • • • • • • • f, • • •i'

~

I.13.

14. Vo1wne of mercury entering half grainsA-lot 11; burn rate 0.60 m/sec; O-lotm/sec; a -lot 1, burn rate 0.32 m/sec;rate 0.38 m/scc .....••••

of black powder:la, burn rate 0.51and ~ -lot b, burn

31

32

<, 15. Relationship between hurning rate and density of blackpowder reproduced from reference 1. Dimensions refer topellet size .......•..•••....... 37

Relationship between flume spread rate and density.Subscripts refer to deviant lot number ..•.•• · . . 39

Figl1re

LIST OF ILLUSTRATIONS (Cont'd)

Page

17. Passageway diameter distribution for whole grains of blackpowder. Dark portion repressed by a factor of 10 . 41

18. Passageway diameter distribution for half grains of blackpowder. Da.rk portion repressed by a factor of 10 • 42

19. Relationship between flame spread rate and surface area.Subscripts refer to lot number: 1-10 deviant lots; 11,75-2, 75-61, 75-44 are GOEX material; 7-11 is CIL material;and Msubscript ~amples were measured by MicromeriticsCorp., others by NSW . • . • • • • • • • • • • • • • •• 43

20. Rel..tionship between flame spread rate and free volume.Subscripts refer to lot number: +, values calculated byequation (3) and", values calculated by equation (4) 46

21. Relationship between burning tir..e and moisture content 48

I. INTRODUCTION

Black powder was made in production mills in Europe as early as1340 in Augsburg, 1344 in Spandau and 1348 in Legnica. The process,traceable to the early B.C. effort of the Chinese, evolved as an "artform" having historical rather than scientific origins. The develop­"lent of the craft has been reconstructed by various authors and excel­lent accounts have been given by Urbanski l and Marshall. 2 The subjecthas been l'cvicwed by Fedoroff and Sheffield3 who provide numerous refer­ences.

In c::isence, black powder has been made by grinding potassium nitrato,sulfur ,Lnd charcoal into a very fine powder. This material is trans­formed into a cohesive conglomerate mass by either forming a paste whichis forced through and divided by a screen, or the material is pressedintll a cah~. Both forms are subsequently broken into pieces. The smalllumps 01' grains of black powder are then coated with graphite to retardthe absorption of moisture and to prevent the grains from adhering.The grains are then screened to a particular size. This process hasbeen standardi ;:ed to some degree, in accordance with prevail inG tech­nology, but the operator adds water, adjusts tomperature, s~lects

grinding time, or changes compression pressure based on pel'sonal experi­en~l' IVhich is guided by individual judgment of color, odor, or generalljl'r~l'ptinn of the condition of black powder as it undergoes its varioustransftll'lllat ions. Su~h judgments arc cx~hanged from experienced operatorto j oUl·neYlllan.

Although the production of black powder was as great as lO.() millionpoullds~ during WOl'ld War I, the advent of smokeless powder diminisheddemand. This fad together with the inherent dangers of pr..:>duction,marked by oCl'asionul explosions, has resulted in closing most manufac­turing facilities in North America. Because black powder still plays animportant role in fuses and ignition devices the U. S. Army Corps ofEngineers has built an Ammunition Plant in Charles';o',m, IN and equipmentIvas installed by leI Americas, tnc. In designing the plant every cffortlVas Illade to modernize the black powder manufacturing process and to makeit as safe as possible. In the planning stage various studies were

Voz 3~

,.,"Ar>tJl1<2' NQ1'iJJzQtz~ EXl'loElivCB" Sea. Ed. Vol z~ [{1:ctOr>y u.n.d MQnufQotul"e~

P. Blakiston'l1 Son Q/1d Co.~ PhiZadelphia~ (1917).

·'B. T. F'edor>orr mId ~. E. She{Field~ .Ena4alopedia 0t Eo.v7Jlosives andRelated Items, Vol ". ~ PATR u700~ Naahnny Ar>oenaL- .. [Jover .. NJ..pr, 8165-B178 .. (1962).

4Al"thl,!1" P. VangeZder> and Hug" S:Jhatt~r .. Hist01"7 of the ExpZosive II1,dUStl'ybl Amer>t' aa, NY Columbia Univel"Dz'ty Press.. NY 1927} •

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conducted to: (1) elucidate and evaluate the ball and wheel mill process,(2) to investig~te new techniques and e~uipment and (3) to compare theballistic properties of bl3ck powder orilinatinl from this and othercountries. The accumulated knowledge was used as a foundation for thedesign of the Indiana Plant. This wor~ was reported in part by theChromalloy corporationg

S BattelleSMemorial In5titute,6 Olin Corporation7and leI Americas. Inc. Battelle published abstracts of SO articlesand bO patents describing the wheel mill process in fine detail. Thisprocess. sometimes referred to as the "standard process". and used in the18bO l s can be currently witnessed at the Belin Powder Works in Moosic. PA.The plant was built in HHl-12 and operated for many years by theE. I. du Pont de Nemours ti Co. The plant is now owned and operated byGOEX. Inc., mld supplies most of the military black powder requirements.

Partide size distributions obtained by "the standard process" ~ere

measured. using optical techniques, by Battelle Memorial Institute,6 as afunction of both grinding time and moisture content. These re~u1ts werecompared to black powder made by another technique, the jet mill process,in which material is ground by impaction created by high velocity airstreams. The jet mill process was developed by Kjcll L~vold9 and isused in Nor\~ay to make black powder. The technique was incorporated inthe Indiana Plant. Using the jet mill, particles are generally one thirdsmaller than produced by the whe,el milL Also, J. C. Alle:110 compared the

5ChroomaUoy C02'poroation~ "A study of Moderni3ed Teohniques for theManufacturoe of Blaok Powdero", PropeZleJ: Chemioal Division, Final ReportNo. DAI-23-0?2-501-0RD-P-43~ Jan 60, Chromattoy Co1"p., IL.

6H• E. Carlton~ B. B. Bohpep, and H. Naok, '~attetle Memoriat InstituteFinal Repol't on Advisopy SeMJiOed on Conoeptual De,ign and Develop­ment of New and Impl'oved Pr'ooesses fOl' the Manufaoture Of Blaak Power"~

Olin Corporoation, Indiana Army Ammunition Ptant, 80 Oot 1970, C'haples­town~ IN.

7J• R. Plessinger and L. W. Braniff, "Final Report on Development ofImproved 'ProOCCEJS foro the Manufao'i-upe of Blaok PotJder"~ RCS AMURE-l09,Olin Corpol'ation~ Indiana Army Ammunition Ptant, 31 Deo 1971, Charles­town, IN.

aIndiana Amrrrw77:tion Pla/tt, "Black Powder ManufaotuPing FaoiUty"~ Vol.1 and 2~ Indiana Army AmmuniHon Plant, 1975, CharlestotJn, IN.

9 ..Kjell Lovold~ U.S. Patent No. 3660546, "Prooess for the Preparation ofBlack Powder", 2 May 1972.

10J. C. Allen, "'!he Adequaoy of Mi Utary Speoifioation MIL-P-223B toAS8ure Funotionally Reliable Blaok Powder'~ Report No. ASRSD-QA-A-P-60~

Ammunition SY8te~~ Reliability and Safety Div, Produot AS8Ur'anoe Direo­torate~ June 1974, pi,oatinny Arsenal, Dovep, NJ.

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effects of different milling procedures at various production facilitiesused in this and other countries.

Other types cf preparation have been attempted which include dis­solving sulfurS by either carbon disulfido or alcohol and mixing thissolution, or slurry, with charcoal and potassium nitrate before evaporating.Another innovation of note was pursued by Voigt ll in which potassiumnitrate was precipitated from solution by adding alcohol in a controlledmanner to produce fine particles.

From the extensive background one general observation made in regardto the production of black pOWder is that the same mlmufacturing proce­dure, using the S3me ingredients, will result in lOt!1 exhibiting differentburning rates. This has been the experience of GOEX, Inc. where fastnnd slow lots nre blended to obtain a particular result. Althouah someof the factors which effect burn rate lire known, the lot-to-lot variationshnve not hcen identified. One attempt to study the effect of 5mall per­turbations wa~ supported by the Product Assurance Directorate, under thedirection of J, C. Allen12 where planned and slight deviations from a nor­mal production run were purposefully and systematically introduced inten lots of black powder made by the Indiana pilot plant. These samples\~cre ll~cd to determine what manufacturing parameters are important ineffecting tho performance and combustion of black pOWder. These lots\~Cl'C termed ~ "deviant lots" and will be described later. The burningcharncteristlcs of these and other standard lots were measured by fourdiffel'cnt lnboratories: ARRADCOM (BRL l3 , LCWSLl4) , ICI Americas Corp ,15

11U• William Voigt, J~., PeZt W. La~~enoe, and Jean P. Piaard, "Proaessfor Preparing Modified BZaok Powder Pez,zets", U.S. Patent, 393'1'1'11,Feb 10, 1976, Bee atso H. W. Voigt and D. S. Downs, '~impZifi,d Pro­aessing of Blaok Po~der and Py~oteohnioaZ Ignite~ Pitts InoZuding Lo~

Res7-due Ve~sions", Seventh InteZ'natianaZ Pyroteohnios Seminar, VoZ. 2,ITT Resea~oh Inst., Chioago IL, JuZy 1980.

12J• C. AZZEln, "Conoept Soope of Work FoZ' MM&'fE P1'ojeot 5'164303 Aooept­anae of CJntinuousZy Produoed Btaok PowdeZ"~ Report No. SARPA-QA-X-10,Novembe~ 1975, Pio~tinny A~senaZ Dover, NJ.

13K. J. ~lite, H. E, HoZmes, J. R. KeZso J~., A. W. Horst~ and I. W. May,"Igni'vion Train and Laboratory Testin.g of BZaok Po~der", ARRADCON-BRDReport No. IMR-64~, ApriZ 19'19, APG, MD. See aZso K. J. Mhite, H. E.HoLmes, and J. R. KeZso, "Ef,feot of BZaok Power Combustion on High andLo~ P2"essu~e Ignite~ Systems", 16th JANNAF Combustion Meeting, CPIAPubliaation 308, Dea 1979.

14£. Shulman, private oommunioation, (data quoted in referenoe 13)~ 15Jan 1978, pioatinny A~senaZ, Dot)er~ NJ•

15nugh FitZer, private oommunioation - Draft report~ '~ooeptanoe ofContinuousZy Produoed BZaok Pol.Jder", 8 MaZ'oh 19'19, ICI Amerioa CoZ'p.,CharZestolAJn~ IN.

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and Princeton Combustion Research Laboratories. 16 Thele results werecompare~ by Kevin White13 and will be pre.ented latet; it was concluded 'that the same tr~nds were observed in each laboratory. Althouah therewere \!ifferenccs in burning rates between various lots, the conclusionwas that smnll perturb{\tions in manufacturing p:,oc.dures do not accountfor tho \!iffcrcncc of a fUl:tor of two in the obseTved flalle spread rates.When these lot~ wore compured with some GOBX, Inc. black powder, it wasinferred that some other unhlentifiod variable must be operative inthesc ~amples.

Tho pCl'forlllanl:C of blad pow\!er, in contrast to its preparation,has bocn ~hal'al'tl'ri5cd in the dassic papers of Noble and Abel 17 - 18 .Recently, Williams' slimmarizoJ burning characteristics and includedseveral fordgn l'efcrcnl:cs. Roso 20 studie\! the performance of blal.:kpowdcr madc frolll I:han:oal produce\! by various manufacturers and concludedthat rcsponsl' could b" traced to vOlatil~ content; he also presented anexcclll'llt I'CV iew article. 2l Kirshenbaum 2 concluded from thermal UTAanal)'sis that c'/en when volatiles were removed from charcoal the sameordor of ignition was maintained and some other parameter besidf:ls vola­tiles affected the ignition of black pl.lwder. He also found that ignitiontOIll}ICra t lire Ivas not a funl: t ion of curbon surface area, ash content norof sulfur content. Further, activation energy was not a function ofvolat ile ~olltellt. Blackwood and Bowden23 sugge:;ted that sulfur reactswith volatiles LIS an initiation step but Kirshenbaum showed that allthree ClJmpoll:.mts, sulfur, potassium nitrate and charcoal, must be

16Neate A. Meowilla, LaP!'!} S. Ingram and Martin SwmIerfi,e'td, ''B'taokPOlJder' l;ualitV AS8ur'mtae FZame Spread Tester", Fina't Report No.PCRL-TR-78-101, LJeo 1978, ~noeton Combu8tio~ Laboratories ina.,t'r'inae tor! NJ.

l?R. A. NoMe and P. Abet, PhiZ. Trans. Roy. Soo., London, Series AVot. 165, 19-1.55, (1875).-

18R• A. Noble and P. Abet, phit. ~ns. Roy. Soo., London, Series A203-279, (1880).

19F. ro/u l iamo, "Tlle Ro te of Btaak POII,der in PropeHing cna.rgsB", Pioa­tillriU Al"'senal Teah. Report No. 4770, May 1975, ptoa'tinny Arsena'L,Dover, 1M.

noU James F:. Rose, "Trwestigat{.on on Btaak PorJder and Charooa't", IHTR-433,

Sept. 1975, Navat Ordnance Station, Indian Head, MD.

21 ,James E. Hone, "13lao/<, Powder' - A Modern Ccmrnentary", 'PrOf1. of the 10thSymposium on Explosives and Pyroteohnios, 14-16, 1979, Frank'tinReeeareh [no t. pl·d Zadetphia, PA •

22Abroham D. Ki2.elumbaum, Thermoohimioa Aota, 18, 113, (19'17).

23J • D. Btaak1JooJ and F. P. Bowden, ?roo. R01:t. Soo., London, A213, 285,(1952).

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present to induce a low temperature pre-ignition exotherm. Perhaps oneof the most persuasive experiments on the importance of volatile. wasthat of Blackwood and Bowden in which they dissolved volatiles from char­coal with acetone nnd applied them to charcoal that was 9S percent carbon.Black powder made from this material had the same behavior as standardpowder.

Clearly. volatiles affect burning rate and Hintze24 shows the rela­tionship. lie recommends 82.S percent carbon content for charcoal andBlackwood and Bowden recommended 70 percent. However. neither workrelates these percentages to a standard initial form of water or ash­free basis and it is not clear that the recommendations can be compare1directly. Both authors do recommend a rather hiah volatile content.However. this parameter cannot ue the only property that affects burningrnte for the deViant lots have diverse burning rates in\orporating the~ame cbarcoal.

In addition to the affect of volatiles. Shulman25 •26 studied theinfluence of small amounts of water. to two percent on ;he burning rateof black powderj this study was ~xpanded by Plessinger. These investi­gations quantify a well-known parameter.

From this discussion it is seen that the properties of c~arcoal areimportant. but the exact nature of the requirements necessary to make agood ballistic product are elusive. Present practice is that charcoalbe made from porous light wood. maple being currently selected. and be oflow ash content. No specification exists citing volatile content butcurrent practice is that it be 20-30%. This specification is broad inthat it requires charcoal which results in a proper performing blackpowder. The specificatirm does not cite the wood. particulars relatingto distillation. or physical properties. Por black powder the amountof potassium nitrate. SUlfur. and charcoal is given but compaction pres­sure is not. Only a density range for black powder is given. Suchcriteria result in a large latitude in allowable variance in the materialsused to make black powder.

It appeared to this author that rather large variations in materialsor in preparation of black powder resulted in rather small but measurable

~4Wotdemar Hintae, EXplosivstotfeJ 8, 41, (1968).

25L. Shu lman, C. Lenchita, L. Bottei., R. Young and P. Casiano, "An Analysisof the Rote of Noistu!'e, Grain Siae, and SUrfaoe Glaae on the Combustionand F'unationing of Blaok PolAJder", Ploatinny ArsenaL Report No. 76-FR­G-B-1S, Qat. 1975, Pioatinny Arsenal, Dover, NJ.

26L• Shulman, R. Young, E. Hayes and C. Lenchita, "The Igniti.on Charao­teristics of Black Powder", ptoatinny Arsenal Teohni.oal Report No. 1805,Sept. 1987J F~aatinny Arsenal, Dover, NJ.

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variations in humina rate. lot-to-lot differences, uliRa the ....II&terials and technique., Wli a doaiunt f..ture. It wal for thelere_sons that anottwr lensitive par••t .... aoupt ad • cadl.ate hy­pothuis was that 'the dear" o! opennels of a Il'ain caul. influence burn­ing rate. Soon th~ study evolved into an investiaation of the physicalpropertic~ of black powder and their relation to burnina rate.

In an attempt to characterize black powder, scanninl electron micro­sco~e photographs were obtained w~ich showed extensive fusing of material.Thi s immediately sunesteel that cOllpaction studies bf performed on pureingrediel1 'tlj to determine what uterial flowed and the functional relation­ship b..:tween flow and applied pressure. In addition the free volwae wasmeasured by mercury intrusion techniques. Furthor. the internal surfacearea was Gbtair.~ from ,the Brunauer, Emmett. and Teller (B.E.T.) gasabs~rption technique. From these several measurements a physical descrip­tion of black powder developed.

II. EXPERIMENTAL

A. Black Powder Samples

Deviant lots. mentioned earlier. were chosen for study as they were:(1) well characteTi1.~d ballistically by four laboratories. (2) made fromingredients supplied by the same manufacturer, (3) fabricated by the jetmill process, and (4) rel':t'esentative pilot plant samples typical of futureproduction techniques. Such samples w~re compared to bhck powder madeb)' the "standard" wheel mill process at GOaX, Inc. The deviant lots weremade from oak charcoal and GOEX. Inc., usad maple. Equivalent compactionpressure~ were used bl both manufact~rers.

Due to the limited capacity of the Indiana pilot plant, their jet­milled meal was moisturized in a wheel mill at Picatinny Arsenal andpressurized at GOEX, Inc., to not less than 3500 psi, or 246 kl/cm2.Fabrication has been described in detLil lS and composition liven in Table1. For this table the carbon content has been rec~lculated on a moistureand ash-frce basis. Also to obtain the hilh and low caTbon content char··coals, three different lo~s of oak charcoal were used. The hiah carboncontent charcc,al was but eight percent areater than that normally usedand t~e low carbon material was 17 percent below standard. The spreadin these values is significant but small. Such samples were compared toGOEX, Inc., and CIL bla~k powder produced by the standard process andmade t..tl.h maple charcoal. The burnina rate datil from various laboratoriesARRADC~'1 (BRL,l~ L~WSL14), and Princeton Combustion Research Laboratories 16are compared in Figure 1 reproduced from reference 13. The results arenormalized to the burning rate data for ~ standard GOEX , Inc., lot, 75-44.

12

...... ,lL'. _" :...... : .........-d ":, . ,a..

"'1'. :.~ -

; - j_,_ __ --J

Irj~j,.:

l'

~

i~

'fABLE 1. UEVIANT BLACK PCWUER LOTS

Lot Density** KNlJj S C.ncoa1 Flue Spread·**

Number Description* g-cm-3 % % \ lIS-I-- - ---

I High KN03l.8b 78.01 8.50 11.95 0.32

2 Low KN031. 74 73.00 10.40 16.30 0.50

3 Poor Agglomeration of Ingredients 1.77 75.95 9.24 13.0:' 0.41

4 High Density 1.80 74.81 9.29 16.05 0.3~

5 Low Density 1.67 i4.94 9.07 14.41. 0.43

6 High Glaze - 0.2% 1. 78 74.88 9.23 14.08 0.39

7 High Carbon - 79.7\ 1.67 74.52 10.13 1~.21 0.36

8 Low Carbon - .lI.6\ 1.70 75.00 10.23 13.86 0.38

~9 Large Particle Size - avg over 25 ~ 1.70 72.50 10.97 13.59 0.34

e".o10 Small Particle Size - avg over 10 ~ 1.63 74.60 10.38 14.02 0.51

11 GOEX - Lot 75-44 - non-staFdard glaze 1.67 74.29 10.06 1~.56 0.60

u- GOEX - Lot 75-44 - standard glaze 1.72 74.05 10.18 15.33 0.53

GOEX - Lot 75-61 0.57

GOEX - Lot 75-2 0.60

CIL-7-110.49

.. '

Oak ahazocoaL in Lots 1-7 and 9-10 azae 73. 8~ aazabon on an ash and moisture free basis•

.... '

BuLk c1ensity

***Open air flame spzoead vaLues (ref 13).

wUZ l~Oc~G'100QG'Wa. 800WN-

t'ct~a: 400Z

20

00

"

4 6 8DEVIANT LOTS

10 12GOE75-44

·,

IIi. •

o!• !

Figure 1. Comparison of burning ratls II measured by flaml Ipread.o (ref. 16); c;.10.ld boIftb. C (rlf. 14); and opln airflame sprlad. a (ref. 13).

14

", " .' ·.. ·t

t

'.

,. I

.

.l

B. Scanning Electron Microscopy of Black Powder and Charcoal

S.E.M. photographs of black powder were obtained at two magnifica­tions, 300 and lOOOX, by John Gavel of the Analytical and ~hysical

Measurements Services Section, E.I. du Pont de Nemours &Co., Wilmingt~n,

DE. C1a~s one Brain~, those passing through a number 8 but not a nUllber4 sieve, were examincJ. They were cleaved in half by breaking the grains,much like slHll'ping a twig, to insure that no tool smeared the surface.The new surface was coated with a 20 nm gold and palladium film; 30 keYelectrons were used for analysis.

Another imaging technique was attempted using an electron micropr~be,

model MS-64 marle by the Acton Laborat~ries Inc., of Acton, MA. rn theseexperiments the ~ample was moved normal to the oscillating beam by a motordrive. The experiments were performed by Ralph Benck of the PenotrationMechanics Branch (rMB) of BRL. Both sulfur and potassium x-ray maps wereobtained simultaneously using two detectors. Benck also analyzed thecharcoal ash, from charcoal extracted from lots 1 and 11.

Otbcr S.r.. M. photographs of oak and maple charcoal~ were taken atthc BIU. by fioulJ fiih\1ons Jr., of the Explosive Effects Branch (EBB), usingan Intet'lwtiona1 Sdcntific Corp. S.E.M. model ISI-40 made ir. Avon, CT.Oak I:h(\ 1'CO;l 1 was l'V;I 1uatcJ as received from the Indiana Atnmuni tion Plant;hLHveVC1', it ,vas Pl'l'-scrl~cnel.l. Charcoal passing through an 80 but held on:I lllll mesh scrl'l'n ,,,as c:'XamineJ. The maple chaxocoal was of a larger parti­de size p:I.,;sing thl'ough a 10 but not a 20 mesh screen and, therefore, itwas ground in 11 mortar and pestle to obtain particles of the same size asthe oak. Bot.h samples were obtained by the Indiana aroup from the HardwoodChat'cl':d Co. locateJ in Steelville, MO. S.E.M. views were obtained Pot 100,150, SllO :I'll! ~lllll)X.

In adJitiun, uak dhlrcou1 was extracted from lot 1 and maple fromlot 11 hlack puwJl'r ~amplcs. They were extracted with water and carbonJisllli'idl'. For lot 11 Inu~lli fications of 150, 350, 750, und ISOOX werel'mp1o)'l'J; similar values were used for lot 1 and they were: 100,250,SOO, and lllllllX.

I'Ul'l' SUll'llr, potassium nitrate, and charcoal were each ground to afinl' ]lowl!c,' IISil1~:;1 Il\llrtar anJ pestle. Samples between 1 and 2 grams wereloaded illto a !'nUn Umer Corp. potassium bromide infrared die, modelIHl>-llll2;l, l\Iadl' in Nl'wark, CT. The powders were individually compressedusing an Illstrllll Corp, material testing instruml'nt, model 2TlIM, maJe inCanton, MA, Tlte pl'ess's cross heads move at various, constant, prl'­sl'1l'l"tL'd !'all's and the small compressive movement of 0.254 nun per minute,,,as sell'ded t',l iusurl' some degree of pressure equilihrium. /\ tuta1load of ~,l)()ll kg cl\l-2 ,or 40,000 psi was applied slowly. At maximumpressut'l' till' lli red inn, of the cross heads was reversed, at the suml' ratl',

15

to obtain a decompression curve. In some cases the process was repeatedtwice to define the permanent effect of the first compression.

One sampl~ of potalsium nitrate wa. made damp by adding four percentcolored water and grinding to a constant hue. The experiments were per­formed by Dominic Di Berardo of the PMB Branch of BRL.

D. Mercury Intrusion Porosit,'.

Internal volume and pore size distribution of either whol~ or cleavedgrains of black powder were measured by Jean Owens of Micromeritics Corp.located in Norcross, GA. The technique subjected samples to mercury pres­sures to 3.5 X 103 kg cm-= or SO,OOO psi forcing liquid into pore~ havingdial,leters gruater than 30A. The grains of black powder were degassed bya 100'C flowing nitrogen stream for 40 minutes. The technique has beendescribed by Orr2? and Adamson. 28

Mercury, due to its high surface tension, does not wet most surfacesand pressure is required to force the fluid into small pores. Hence, thepore size is directly rel~ted to appli~d pressure and the relationshipis given by equation 1.

pr • -2 a cos (;) (1)

where P is pressure, r 15 the radius, a is the surface tension of mercury(taken as 474 dynes cm- ) and (;) is the contact angle (taken as 130' formost substances).

The distribution of ~uch openings is given by a dist.ribution func­tion, D(r) I

D(r) II f ~rYLr ~

(2 )

..I

.oj

where VT is the total penetration volumc and V is the penetration volumewith openings greater than r.

"'1U Clyde Orr Jr•• Powder T6ohnot., 3. 117 (1969/1970).

,~8Arthur W. Adamson. Physioat Chemistry of SUrfaces. 2nd Ed•• Inter­science. NY, pp. 046-649, (1987J.

1h

E. a.E.T. Surface Area Measurements

In addition to the mercury intrusion measurements, MicromeriticsCorp. also determir.ed surface area by a single point a.E.T. techniqueusing degassed whole grain samples and argon ga$. This techniqu~ hasbeen described in several texts, for example Flood,29 where surfacearp.a is related to the number of argon atoms required to form a liquidfilm on a given surface. These measurements were extended to othersamples by Eleonore Kayser of the Naval Surface Weapons Laboratory, NSW,in Silver Springs, MD, using the same type of Micromeri tics equipment,model 2205.

P. Density Measurements

Even though density is defined dearly as gm/emS , thevolume for powders and compressed masses can be ambiguous.rea~on some experimental approach~~ will be Jiscus~ed.

mcasuremen": ofFor this

. \~

1. "'I'LlI' Density" is u term that has been used to describe theweight of a powder ~r objects poured into a known geometry and allowedto settle h>' one or more :,tentle means su~h at "tapping". Such valuesarc not u!\ed in this !\tudy.

2. "Bulk \len!\ity" depicts the volume clement inscrihed hy its outersurface. The volume is measured hy sinking a powder or ohject into mercuryat atmosphcrh: pressure. SUl:h vulues do not include pore volume andlIrc given in Table I as reported by lIitler.

3. "Truc \lensit)'" Is obtained by measurinA the volume of a'.l objectas l'4ual to tile amount of non-absorbed gase~ It displaces. tn suchilll'aSlirements helium is lI~uully introduced into an evacuated sample amifills small pores. Similar values arc obtained by usln~ ether as thedisplacement fluid for evacuuted samrles,~O or using mercury di~placementat vl'ry hl~h prc!\sures of mercury. In this study Itn ether dil'p:l1cemt"ntmeasurement WtlS made on non-( '/acuut,'l! samples to cst imate the samples'true density. Flow of l'thl'r into the sampll' was aided by placing thepycnometer filled with hiack pow~~r and ether in an ultrd~onic bath.

I I I • I{LSIJ I.TS

Four hlack powder Rumples \~l'I'l' l'hOS('11 frum thl' deviant lots ,'orexaminat ion. I.ots land hare sampll's having slO\~ flaml' sprl'ad ratl'!'\ of

.~[} .ro:. AlW0n FZood, Ed., The SoZ U-Gao Inte'l'[aacJ Vol. 1, Mal'aeZ Tickke'l'Ina., NY, (1967) •

3JR• M. M~rntOL111 mul A. P. StuaY't, Can. ,J. Rca. B"~1, 124, (1946).

i

. l ~;

0.32 and 0.39 mls as contr~sted to lots 10 and 11 which have fasterflame spread rates of 0.51 and 0.61 m/s. Further, lots 1, 6, ~nd 10are jet-milled oak products whereas lot 11 is a standard wheel-milledmateria! of GOEX, tnc. The S.E.M. microphotographs are &iv~n in Figures2. 3, 4. and 5. Stereo views were made but add little to the detailal ready shown and therefore aj,'e not presented. Potassium ond sul furx-ray maps were obtaiued but the concentration profiles did not showsharp boundaries a~ prominent features. The problem is the averageparticle size in about 15 microns or less and th~ x-ray maps depicted anaverage c0ncentration to a depth of approximately 30 microns. Thereforesuch analysis represented an average concentration throughout the slab.For this reason those views have not 'Jeen included.

The microprobe ~xperiment was abandoned for black powder surfaceanalysis. for although the sulfur and pot::,ssium x-rays were recordedsimultaneously. and gave strong signals, the electron beam created areaction path und the data could not be relied upon to depict theoriginal ~ample. However, the microprobe did analyze the ash contentof both extract~d charcoals and calcium was found to be the dominantspecies al~ traces of silicon and phosvhorouz were noted. No othermetals were detected. The ash content of maple charcoal was 2.3 percentand 11.9 percent was found for oak.

The S.E.M. microphotographs of the raw materials, oak and maplecharcoals, are given in Figures band 7. Extracted charcoals from blackpowder arc shown for lot H in Figure 8 and for lot 11 in Figure 9.

B. Compre~_~.ion_.of Sul~ur, Potassium Nitrate, and Charcoal

In the manufacture of black powder, damp meal typically containingmaterials of less than 25 microns, is pressed into a cake where variousfabricators have used different compaction pressures. tn aeneral, apressure is selected which will result in a finished grain density ofappro~imatcly 1.7 and GOEl, Inc. employs a pressure no smaller than 24bkg cm~ or 3,500 psi. All of the S.E.M. microphotographs, Fiaures 2-5,show considerable plastic flow and fusina among particles forminaextensive aKglomeration lllrgcr than the orisinal particle size. Thereforea compaction experimunt wns performed to determine the relntionshiphetween flow and applied pressure.

TIll' rl'sults of compressing pure ground sulfur, lJui:.3ssium nitrateanJ char~oal an~ given in rigure 10. The relationships SI.l')wn can belinearizeJ by presenting the logarithm of applied pressure ,lS a functionof comrad ion. 'I'll(' density of this sulfur cake was 2.00 gm/cm~ and thatof th:- Jamp anJ Jry potassium nitrate cukes were both 2.08 gm/cm:\.\.itcratlll"l' valucs:"'i arc 2.07 and 2.109 gm/cm 3 for t.he·;e compounds andthus, at the maximum pressure used, no significant voids exist in ejthe~

materia 1. In these cases the decompressIon curve is almost verticalshowing little elasticity anJ recompression forms a small envelope aboutthe decompression curve. The oak and maple charcoal compression curves

is

&u••S

~

....~

0...J..'-(\J

"i~~

UIU....eo

.N

QJ

'-::::l.,. C'l.~

§ 1.1..

U.-s8-

,.

..~_. "':'-.

~

..,a

.9•t1i.~U10~

ClCl

•C")

"...::Ic:n'"Ll...,.

~u.-E

00-

':0

0.-+J

.9•tie.~u"'.-co

•..Q,I~

="'"

It:

u.-E

8-

~'','i

~ j

;:-1, I

1·A-'II I1,

, t~E

j0

I."

1

21

..

--.....9•tI,)/.u..-a:l

It)

cu..:lI.,.-&.&.

~U.-e8-

Iu..~E

~

22

...__ . ~._._.

"~"'aai:wi~"iir" ...

,I

OAK J--f- 100 microns OAK t---I- 100 microns

Ffgure 6. Oak and Maple Charcoals

1--1- 100 micronsMAPLE100 micronsMAPLE

r ...~I

; t

"!I

::1, !

'. ,

',1

"'-t:',

r $." S ; Q2; L :. - _

t---+- 5 micronsOAK1-4-20 microns

~4 ., ...4......, .J'., .. ..........".

-.; ~ ~~........~~~... .. """...y.-

OAK

'I

'-~:,

'j

Figure 7. oak and Maple Charcoals

I

c·I

~, I• j

. ~

J'j

I1I

'd. Ii<.j

;,

i #

4J4-I~j

./

r ....~

MAPLE...

t--+- 20 microns MAPLE I--f- S microns

e ~ 4:; is ' ...,. .... "... .-.r +4 p.""'T'~. .. .'

I'

I--+- 100 microns H- 30 microns

I-+- 20 microns

Figure 8. Oak Charcoal ~tracted from Lot 1

;;

IIl.

~. -

t--I- 10 Microns

,--

~.. -i-'/­

"M-~,f'

-~-- . ~ .-.r-i . . ..'

'~.i ~ -W ':-.....;..~.' . 4l -' •. ~-~ ~

,1.(' . ~ _, ,. ... ' '" " "'1. , ~ . I . "'

, . ""' It.;\ .r:-

~.., " .' ,.

. .... -. - _.'-' -...~.' -

~_. ,r~ ~ _.~. -y '.~ ~', . ".... • 'h... - ~, '""A...... ' ..... '-~,. ~.,

~.. ~. '. ., -'\ \-.1',' . ~,->...I~,,- -' (',' ....' ~~--

f-,jtil

,I

i1lt

i11<41

J ';~

~

,if

2()

. ~ .1: .

A i.'MS ... $. """4 .~5 ",,:11.-.....,. ,~~.'.--" .. -~_., - j ..

i._ .iL. .......,. OIl: ~ - ." 'c." -OM _ _ - - _.- _. -~ - --~ -- -- ._- _. _.- .'~:J

10 20 ~O 40 50 60 70COMPRESSION (I)

r·~

--.J

-NE~

~-wa:::::>(,/')enwa:CL

4000f

r3000

00

KN03wet I Idry

III,IIf

ISULFUR

lCHARCOAL

80

Fi1ure 10. Effect of pressure on potassiuM nitrate. sulfur. and charcoal

were identi~al, but a compre~scd Jens! ty of 1. 01 gm/~m~ wns measured forthe maple ~harconl and u uensity of l.lh gm/cm~ was measured for oak toan ac~uracy of 0.5 per~cnt. Values were obtaineJ from the sample weightnnd die dimensions at mnxlumum pTessuTo. The decompression curves forboth samples showed considerable elasticity. Interestingly, each samplewas removed as a powder from the Jie and ohvlously the o:'ganic~ did not(ll't as a binJer.

In an attempt to intl'rprct the compression density vuiues, the~Ien::;itll's of hoth charcoals Wl're measured hy an other displacement techniqueusing a pycnometl'l'. The Jensi ty va lues were O. ~IH and I. 17 gm/cm~ andWl'l'l' accurate to l.ll percent. They Wl'ro elllHlI to those mea sured In the~'l)11Iprl'ssiol\ expel'im'.'nts. After compression, the charcoal originallypassing throu~h an SO hut not a 100 mC'sh screen, W:JS again sieved andthl' rl'sults arl' ~Ivl.'n In 'I'ahll' 2. The valUl'S show that many pieces ofdWl'coal wcrl' hrllkl'n h}' the large uppl ied force.

'I'Al\Lli 2. CHARCOAL SIUVED AFI'LR COMI'IHiSSION

I·

Screen 5i:oMesh Unit~

100120200340

*~ by lJeight

C. Mercury Intrusion Porosimetry

Oak·oo

2412~8

26

Maple·%

518

2615

.• I.~

\. .\

Three different samples of 1-2 grains of whole grain black powder,lots 6 and 10, were evaluated to determine the reproducibility of boththe sampling and measuring techniques. Data aTe given in Figure 11 and12 showing the cumulative amount of mercury forced into pores of diff~rent

radii by various pressures. The d. "'1 have been normalized at 200 psi 01'

l~ kg/cm2 and shows a good degree of reproducibility. One sample eachof lots 1 and 11 wag evaluated and this data is given to~ether with arepresentative penetration curve for lots 1 and 6 in figure 13. Thesesame four lots were also evaluated by cutting the grains in half. TheseJata are given in Figure 14. 1" all cases the cut or whole grains wereintact after pressure was released.

11. ILE.T, Surface Area Measurements

The surface area of whole grains was measured by ~ ~.~.T. analysis .All of the deviant lots were evaluated as well as GOEX, Inc. and elL

28

Ad

PORE DIAMETER (micron.)

.06 r-_'.,.,.01"'l""l""".........--.~l""- ......0.....11'"P'1" •0_.:I-P\_,...., ,.......~_.....OO2

.05 ~

~-~ 1.e 0u • 4

Z .."g .f.U')::)

.03C' .,Z

"~ ...~

.02 ..,ul ' C' ..

W " ..~

" • ••" • ••01 ••• ••" ••.

fIf

100 1000 10 ( psi) 100000

I ''tIll , "~'I'10 100 ' . ') 10000

PRESSURi: \ ..- '.: m2)

Fi3ure 11. Volume of mercury entering three samples of black powder ~

l.ot 5. \~.

.,

.oj

a •, 0\

...... '" ..

, §M

PORE DIAMETER (",ieron,)

.061.0 O. 1 .01 .002

••

I I •I

•- •~ •... .0. •" • '+-~ • • +~':) .C3 ••• +9+++~... • -Z- & ..-~ •.02 ••• +w e+~ •

.01 • ++

+

•100 1000 10000 ( pli 100000

L$ , , , It '

" 1''' ttl,"10 100 1000 10000

PRESSURE (kl/c,.,2)

",

. '-:1

, '\

•, I

~ .'o!

Figure 12. Volume of mercury entering three samples of black powder ­Lot 10

30

r'

~..... .. _.j -...,,; '.

.001DIAMETER

>~.02u~

w~

.01

DIDo r' , , , '1000 ' " ;0000 (psi) 100000

I """,,1 "",,"1 'I "~,ltd10 100 1 000 10000

PRESSUR~ (kg Icm2 )

zo-en~.03«.-Z

.06rIII

.05 r-II

at I,.,... 04E.

u-

'J'-

'''~

,

II~.'~t;

I

rigllrf: 13, Volume of menury entt"dng lIIholt? 91-.11n5 of t'!1.l(I.. p\>wJrl':A -lC't 11. biJrn r.lte 0.60 _/sec;• -lnt Ill. hurn r.lte O.Sl III/se(~. -lot 1. blll-" t'.lte l1_J~ l'1'se~-~ .lnJ9 -l."t 6. burn r3te 0.35 m/sec,

.. :p-~'

.=;J...•__....... :=:-. _M. .... -

.001PORE DIAMETER (microns)

.10 .01

o100 1000 10000 (psi} 100 000

I ",."", " "",,1 I II"""10 100 1000 10000

PRESSURE (kg/cm2 )

>~.02uGl:W~

.01

·06rIIL.05,II

D I~(Me·

u-zo-~.03Gl:I-Z

:,.r~

.~

I!;i."j

IFil)ure 14. VolU1l1e of mercury entering hal f grains of bl.1d. powder:4 -lilt 11. burn ,'ate 0.60 mIse.,;;O-Iot 10. burn rate 0.5J m{sec; a -Jot 1. but"n '"ate O.3.? m/sec ...md" -lot 6. burn rate 0.38 m/sec.

,

f

II'

I'II

[

'. .

black powder. One lot, lot 6, was examined in detail to determine thev~riance and preci~ion associated with samplina and measurement. Thedata are given in Table 3 and surface areas ranaed from O.S to 1.0m2 gm- l • Each individual sample waf evaluated at least twice.

E. Density Measurements

The density of whole arains of black pOWder was measured by an etherdisplacement technique ~nd values are given in Table 3. Th~y weremeasured to an arcuracy of one tenth of a percent.

The ether displacement density of charcoal extracted frolR lot 11 was1.43. The densities of the maple and oak charcoals supplied from theHardwood Charcoal Co., were 1.01 and 1.16. Reproducibility was as notedabove.

IV. DISCUSSION

A. Black Powder and Charcoal S.E.M. Measure~

The microphotographs of deviant lots 1, 6, and 10, made by the jetmill process, look much alike. They are shown in Figures 2-4. Eachfigure shows two differ~nt views of a particular grain and these viewsare shown at two different maanifications. The view at 300X was attemptedto get a general representation. A smaller subsection is shown at lOOOXto provide greater detail. Higher magnifications were recorded but theylose the general natu~e of the features shown. Sulfur and potassiumnitrate cannot be individually discerned; however from the relative abun­dan~e most of the features represent potassium nitrate.

Figure 2 shows a large isolated charcoal particle; clearly, compres­sion did not fill its pores nor did it crush the charcoal. Thus in thi~

instance incorporation of material into the charcoal pores, a processthat has been ascribed to the wheel mill process,S did not take place.In all figures considerable plastic flow and particle deformation areshown and many con~olidateu regions exilt that are much larger than theoriginal particle size of 10-15 microns. Figure 4, deviant lot 10, showspart ides which appear more intact anet are individually more discernable.Also the degree of plastic flow seems less. This leads to a greateruegree of openness between particles.

The S.E.M. photograrh of the GOEI, Inc. ball milled material, lot11, Figure 5, Is dift",re,lt from the thl'ce-jet milled samples. Luriedumps of material are (,bserved as well as large void reiions. Againone piece of charcoal b evident and its pores are not fllled, nor is itcrusned. The pores arc ~.8 ± 0.9 microns wide. In general, materialseems to have flowed around the charcoal and the photograph shows almostgeological folding. Stress lines and spherical pockets are noted in

33

....,\

...............,..,...~.- .........--.. ~. -_.-_ .....

TABLE 3. SURFACE AREA OF BLACK POWDERAND EntER DISPLACEMENT DBNSITY

Surface Area* Surface Area** Densit~

Lot Number m2 p-1 m2 p-1 p em-

1 0.50 0.5880.53 0.588 1.91

2 0.730.80

1.87

3 0.540.58

1.88

4 0.0600.060

1.89

5 0.580.58

1.85

6*** 0.50 0.5880.55 0.587 1.86

0.520.570.530.510.62

t0.52

7 0.550.58

1.85

8 0.520.52

1.83

9 0.b70.b3

1.82

10 0.6b 0.6390.<>2 0.630 1.85

0.b6

GOEX - Lot 11 0.82 0.8010.7b 0.796 2.02

GOEX 75-44 0.850.850.82

GOEX 75-b1 0.710.73

GOEX 75-~ 0.71O.b9

ell. 7·~.i.0.580.57

, \!•NSW

••Mic~mertic8 Corp.••• •AveraGe ~s 0.55 ± 0.04.

34

• l~

\ .,i

consolidated regions. The grain is not as homogeneous in appearanceas the jet·milled gruin.

In summarizing the S.E.M. microphotographs, compaction seems to forma fused con~lomerate mixture laced with a maze of interconnecting passage·ways.

The S.E.M. microphotographs of oak and maple charcoals are given inFigures band 7. Oak charcoal appears as separate lumps having a clearlydefined cell structure. The maple sample looks torn apart, perhaps bythe grinding action of the mortar and pestle. However, both samplesshow extensive cell structure and broken and chipped pieces dominate.

One series of S.E.M. microphotographs of oak, Figure S, which wasground in the jet mill and extracted from lot I black powder, Figure 9,looks similar to maple charcoal obtained in the same manner from lot 11ground in a wheel mill. The particles seem tc be of similar size and theonly difference is the maple appears more rounded. No large charcoalpieces are evident in the maple photograph as was seen in its black powdercounterpart but the view may not be totally representative.

In summary, it appears that grinding by either method produces afine powder which has a multiplicity of edges, broken pieces and con·voluted surfaces. The grinding process breaks down the gross structureof charcoal, forming pieces and fragments such that the two charcoalslook much alil(e.

Il. Compression of SUlfur, Potassium Nitrate and Charcoal

Noting the extensive flow in grains it became desirable to quantifythe effect of pressure on black powder meal. Damp meal, that is generally4 percent in moisture, has been pressed into a cake using various compac·tion pressures. Values of 1900 psiS (134 kg/cm2) to at least 3,SOO psiSl24b kg/cm2)8 has been employed and some work was done at 8,000 psi31lSb3 kg/cm2). The range of these values raised the questions, "do thesecompaction pressures span the individual yield points of the ingredientsand is a parti.cular pressure threshold required to induce plastic flow?"To answer these questions an experiment was performed to determine ifthe change in volume, or plastic flow, was uniform as the applied pres­sure was increased.

The effect of pressure on the pure materials was determined andshown in Figure 10. From the curvature, it can be seen that eachmaterial flows throughout the applied pressure range. This is areminder that the applied pressure is a global value but the microscopicpressure exerted between particles can be much greater. One compression

31Memoriat Des ~udres Et 8aZpetreB~ Vot. 8, Chapter II by M. Vieitte,Gautnler-vattars Et Fits, zmp~eurB-Librair~s, Paris, pp. 268-391, (1893).

35

curve using damp potassium nitrate, four percent moisture, lies wellunder its dry counterpart showing that water reduces friction, allowingparticles to slide. Thus, applied pressure and water content are coupledpheldmenon which govern grain density.

It was noted that both potassium nitratd and sulfur formed smoothglass like surfaces at the die faces. Such a surface could seal the pelletand this effect could explain why black ~owder pelletized in a pellet pressexhibits slow relative quickness values. Additional ~escriptions ofthis effect can be found in the Ordnance Explosive Train Handbook32 thatdescribes the bUY'uing of a train of several pellets as a succession ofpuffs caused by 'Jurning through the "glazed interface". In such appli­cations, these effects are reduced by pressing pellets as interlockingcones to minimize the e~fects of burning through a sharp boundary.

In addition to the s~rface effect of pressed pellets, there is adensity profile that should be considered when pressing to a given graindensity.

The charcoal compression curve is similar to that of potassiumnitrate and sulfur. From the facts that bulk density at maximum compres­sion and ether displacement density are equal and that compression frac­tures charcoal (Table 2), it is clear that pressure fractures some ofthe charcoal into smaller fragments which then bend elastically to fillthe die leaving very little space between particles. With a density of0.99 for maple and l.l~ for oak charcoal, both far removed from theamorphous carbon value 3 of 1.8 - 2.1, it is concluded that the densityof charcoal reflects an open structure.

The compression results show a gradual change in volume with appliedpressure. This reflects that applied pressure is a global value and theassociated microscopic pressure between small areas of two touchingparticles is much greater. 'Che smooth exponential curves show no sharptransitions that could be associated with yield points nor are anythreshold values indicated.

The effect of compression on black powder meal is yet to be done butthe effect of pressure is to increase density. Vieille31 in 1893 demon­strated the relationship between black powder bulk d~nsity and burn rate.The data was reproduced by Urbanski l and his graph is given in Figure 15.ObviOUSly the data relate to a process and materials different from thoseu5ed today. but the trends should still persist. This same type of

32NavaZ Ordnance Labo~to~y, Ordnanoe EZp!o8i~. Torain De,ign.~B Handbook,NOLR 1111, Ap~il 1962, Navat OitdnanoBI4boMtOJ'Y, Miite oak, MD.

3'~Robe~t C. West, ed., Handbook of Ch_Bt~ and PhI/Bios, 61ct Ed' J '!heChemioaZ Rubbe~ Co., ctet'etana, Ohio (19 -19?1).

36

100....-----.-----....----.......----...

20

10.5 mm

SLOW BURNINGIN PARALLEL lAYERS

~__---3.s mm

2.01.91.8DENSITY

1.70 ......----"------.....----......----....16

Figure 15. Relationship between burning rate and density of blackpowder reproduced from reference 1. Dimensions refer to pellet size.

37

t J.'-,

, . \~

. \ ..'

relationship was shown to be operative in pyrotechnic mbtures whereburning rate was given as a func1.~on of compaction press\lre. 34

Vieille investigated the large density neighborhood of 1.44 to 1.85.In ~ontrast, present experiments, usina material that was available,definc a more rcstrictive neighborhood and the parameter is not illus­trated as dearly. Since VieiUels reference is not readily available,the liherty has been takcn to translate his summary. This translation\~as undertaken hy El i Fl'ccdman of our laboratory (BRL-Applied BallisticsBranl'h) :lnll is givcn as an appcndix.

The flamc spread rate and densities for the deviant lots, given inTahle 1 arc shown as a scattered presentation in Figure lb. A functionalrl'1ationship appears to exist but its exact nature is not given by theselimited data. Thl' scatter leads to the belief that I.:ompression condi­tions w<.'rc not identkal; however, it is clear that flame spread rateJccrca~cs a~ density increases.

Co MCrl~Ur)' Intrusion !'orosimettr

El\uation (1) relating pore size and applied pressure presumes thatthe pores are a collection of right cylinders of different radii. Inpractice small openings exist leading to a larger volume element. Sucha situation has been termed an "ink bottle effect" and when encountered1\'111 1cad to an overestimate of the number of pores that exist at aparticular radius. For loose powders, corrections are attempted bymeasuring the mercury :~xtruded as a sample is depressurized. In accor­dance with equation (1) the neck of the "ink bottle" will elnpty as wellas the "bottle" itself but at different pressures. For compactedmaterial, such a black pOWder equilibrium may be too slow to attempt thiscorrection depressurizing technique. These problems should be consideredI~hen examining the intrusion data and the indicated radii should be con­siJered as approximate values. However. the mercury volume entering agrain is exact.

In examining the S.B.M. microphotographs of black pOWder many voidsarc apparent with radii of 10 microns or less. For mercury to pene­trate the grain and reach these voids it must intrude through passage­I'tars that are small and are not particularly apparent in the view of theplane presented. Therefore, in filling such a void throueh a smallpassageway the mercury will fill the system indicating a pore volumehaving the radius of the passageway. The mercury penetration data,including this effect, arc given in Figures 11, 12, 13, and 14. All ofthe data have b~en normalized to 200 psi or 14 kg/cm2, Three differl:!nt

34A• A. ShidLovskU, "PrincipLes of Pyroteohnios", Air Foroe SyBttlmBCommand, Report No. AD-A001859, 23 Dot 1974, Wright Pntterson AFB, OB,TransLation of Iad Masimostroyeniye, O~vy Pirotekhniki, 3rd Ed.,Noscow (1964).

38

: ,: ~--

". Ji.

r',a ..414$. . ~,_ T' .....,r- .':"~. ,--.,. ·v .~ r't •. ~ .. -- .".• LjELO( ¥f .... , -: ." - . . ~

.._ .. . ....... ~ _-, ._. ", .. _. .c. ; .

I-

I .80

-~.70 T- +11

:~ w 1~

. t-

\

«i

a:: .60I

,j

:i

'~ ~ 0

,:;,0 «

It.O

~ .501-T T+ 10 +2.1 .1

U')

~ .40~T+5 T

1 83+ T T

J. +6 + 4:; 7 IT .1 .1

.30I I

.L + 9

I I I ,1 I I I I I

1.60 1.70 1.80 1.90DENSITY (g/cm3 )

Fi9ure

16. Relationship between flame spread rate and density. Subscripts refer to deviant lot n~hber.

~

i ,. I

". II

."

whole grain samples of lots 6 and 10 were evaluated, Fieures 11 and 12,to determine the reproducibility of the sampling and measurina technique.The penetration data for these samples shows fair aereement and most ofthe mercury entered through passageways between 0.1 and 1.0 micron;meter. The experiment was expanded to include lots land 11 and thewvdata are presented in Figure 13 for whole erains. The experiment wasrepeated on new samples of these lots where the erains were first frac­tured in two. The penetration volume is presented for half erains inFi~ure 14. The data for lot 10 appears to be in error, and for this~amrle some of the grains may have been crushed by the applied pressure.

The mercury intrusion data for the four lots of black powder arenenrly the lHlmc for either whole or cut grains. neither group showinemajor differences in penetration pattern. On this basis, it is concludedthat the grnphlte coating does not seal the grain to pressurized mercury.The two experiments also show that mercury must be able to reach the in­terior of a grain since cut and whole grains host the same v~lume ofpenentration. If mercury intrusion had been related to the black powder~urfacet then penetration between whole and cut grains would have beenapproximately proportional to the ratio of the surface a~ea of a sphere totwo corresponding hemispheres or 2/3. This was not found to be so andthe conclusion is that th~ mercury penetrated throuehout the grain.

The distribution of pasngeways was calculated using equation (2)and the data of Figures 13 and 14. The calCUlation is primarily depen­dent on the slopes shown. therefore, it is not affected by the normali­:ution. The distribution is given in Figures 17 and 18. A correlationexists between the number density of passageways between 0.2 and 0.1micron and flame spread rate. No such relationship was evident for thesmallest of radii and this range will be discussed later.

O. B.E.T. Surface Area Measurements

The intrusion data can be used to calculate internal surface areabut because of the "ink bottle effect" the result would be suspect. Forthis reason the surface orea was measured by the B.E.T. technique andthe results are given in Table 3 and plotted as a function of burningrate in Figure 19. The standard deviation for four samples of lot 6 is6.6 percent and similar agreement on replicates of the same sample wasfound. It is clear that an increase of internal surface area increasesburning rate. The graph, Figure 19, contains several markedly differentblack powder samples including the jet-milled oak deviant lots, ma})leGOEX Inc., powder and one CIL sample. The latter two producers used theball-wheel mill process. Overall, the samples appear to follow the samefunction even in the small neighborhood tested where the density of blackpOWder does not vary to any great extent. It remains to the future todevelop a broader nei~hborhood for :nvestigation. Under these constraintsthe relfl,tionship between burning rate and the deeree of openness of agrain of black powder seems reasonable.

40

F+ 4::'+.cq~;e~tt!;S$'- ~E\ ...... i ._-

1.0

-

PORE DIAMETER (mi'iOOS).10 .OJ .001

~....

.6

.5

.4

-.3a:

0.2o£.1ot= 0,.3u~ .2&L. .1ZQ .3,0I-

~ .2-~ .1C/)

o 0,.3

.2.10

100 1000 10 000 (psi) 100 000I ," , , , " I '" , ",.1 ". , '" ,I10 100 1000

PRESSURE (kg/cm2)10000

Figure 17. Passageway di_eter distribution for whole grains of black powder. Dark portionrepressed by a factor of 10.

. ....- .. ,:,,:, .

_&. _ :.4-.:~ __.! ... _ _ ~ .''''

.001PORE DIAMETER (microns)

.10 .011.0

Z 0,.3o~ .2u~ .1IL .3, 0zQ .2I-

~ .1-~ 0,.3eno .2

.1oL..rZI?2,~Ld

100 1000 10 000 (psi) 100 000I '" "",1 "",1,,1 • I 111111'10 100 1000 10000

PRESSURE (kg Icm2 )

.5

.4

.3

~ .2-o .1

~t..>

••

Figure 18. Passageway di_eter distribution for half grains of black power. Dark portionsrepressed by a factor of 10.

.;.~..:.

, .... 4o...t _ .....

,-..;"

,r"~

0.6 ~ 75;21IT++

11 1111M-~

~ +E 1 T-SO.5~

7-11 TT+

T 175-••T .... 75-61

lOMlll0+

+ 120 Is<tw

3 TQ!Q.

tI h(CI)~

tH8

~ 0.4 T +1 ++ 9<{ + 1T 11 r~ 1LL +6M

71 +

~ fl0.3

0.5 0.6 0.7 0.8 0.9SURFACE AREA (m2/g)

Figure 19. RelationsMp between f1a~e spread rate aM surface area. SUbscripts refer to lotnwBber: 1-10 deyi~nt lots; 11. 75-2. 75-61.75-44 are GOEI -aterial; 7-11. ell ..terials; and Msubscript .easured by Mic~eritics Corp•• others by NSW.

The surface area of charcoa1 22 is about 1000 .2 am-l and sincec~arcofl consititues 15.6 percent of black powder, an upper value of 156m gm- would be expected. The measured values are much less, about0.5 to 1.0 m2 am- l • Therefore, it is concluded that almost all of thecharcoal particles are sufficiently sealed to greatly reduce gas absorp­tion. This could explain why burnina rate wall not found to be a functionof the original surface area of charcoal or other carbon materials. 22

It nl~o should be pointed out that the surface area measuremen~s

~ere extended from the original four samples to include all of the deviantloU. This was performed as a matter of convenience rather than pnfer­~ncc ov~r the pore size measurements, for at the time of analysis it wasmor~ expedient to extend the surface area measurements.

E. nensity Measurements

The toUl free volume can also be calculated from the bulk densityof bind powd~r, (nB/p,), the density of the spparato ing,'dients, (Oi),and pl'r~:cnt composition. Such values were taken from Table 1 and thefollowing relationship, equation 3, was applied to a 100 gm sample. i\!lh"nd moisture content were not included.

free volume. (3)

Using a density of 1.17 for oak and 1.43 for maple charcoal (determinedfrom charcoal extracted from lot 11) the total free volume was calculated.Values are given in Table 4 and Figure 20. They incorporate both isola­ted voids and accessible volume elements. Equation (3) can be used toshow that the density of charcoal is a sensitive parameter that affectsthe free volume of black powder when a particular compression pressurei5 selected for manufacture. Moreover, compressing black powder to aparticular density using different density charcoals will produce grainswith varying degrees of free volume. One problem yet to be addressed isthat no knowledge exists on the density variations for lot-to-lot pro­curement of charcoal. If a variance is found, compaction pressure andgrain density will have to be adjust~d accordingly to obtain the samefree volume or a particular density.

In an attempt to measure the volume accessible from outside of thegrain, the true density (Or) was measured by an ether displacement tech­nique. These values and the bulk density (DB.P.) from Table 1, wererelated to the free volume for a 100 gm sample by the equation:

1. I

~

1000-­B.P.

• !QQ + free volume.DT

44

(4 )

... :t •.,

.-----------..-~_.- __-=-c=--=__,...".",.,. ,..,.,.."_,.,.",,,. _S"'!ii 1 iCiJ&iA ~

... ~

dt.- .. ' ..~ _A.__ .

'.1l!"'".. '.;,.

-e -

TABLE -L FREE VOLtJoIE IN BLACK POWDER

I Lot Eq~ation (3) Eqtp>tioT. P; ~rcurv Intr,sion- Mercury Intrusion-

Number Lm-' /l 00 gm ca~/lOO gm to 0.1' p cm3, 100 gm to 0.003 p c.3/100 ~

1 2.22 I.-ll 1.3 3.9

rl

2 3.61 3.99

3 -t.6i- ..,.,.), ...-

4 1.fH 2.65

5 7.79 5.93

6 3.93 1.·:2 1.0 5.1

~ 7 6.36 5.92~

8 6.2C ~.18

~ 9 7.23 3.88

10 8.70 7.30 1.2 -1.1

11 &.64 10.21 3.0 t.-I

~,~=",...;=. •... - .. ~a:.. _:-iiJJIt .. _.... _- ----...

Figure 20. Relationsh': t,etween flatle spread rate and free volume. Subscripts refer to lot ...ber:+, Ya~Yes calculated by equation (3) and~, values calculated by equation (4).

102 A 6 IFREE VOLUME (%)

o.. 2' , , , , , ' , , , ' ,

o 2 A 6 I 10FREE VOlUME (%)

-..e .6~ +11 I 0n-w

~ .51- +2 +10 I 02 0l()•0

I~ g.+ +5 050'

if;+3 030 A 06~6 ~ +a

+7+, +9 0, 09

~..Ii~~

iIi:

5I· o.

rIr ,1-':i

;

1-·:., ._ i-',' -¥

- . I.~: • :Ii;

I"Hi I,

i);,:,. ,

i '\ ,I

"I'I

\ ".- ItI ii'

I'

These values are listed in Table 4 and in Piaure 20. Comparison of thefree volumcs obtained from equation (3) and (4) shows that in all cases.except lot 4 and lot 11. the total free volume including voids is largerthan that l1c~'cssiblc from outside of the grain. These volumes can be~ompareJ to th~ mercury intrusion valucs. One comparison is to relatethc VOllllllC of mercury IH,'nctr:\tinR through passageways lar~er than 0.1micron, a plateau in rigurc 13, to the density derived values. Tn this\"'a~l', till' merl..'llry '~aluc~ arc smaller and this is reasonahle as small dia­lIll'tl'l' pllrcs have not hcen penetrated. IIowcver. examining the small<'stl'adi1 of U.IlU"~ mh'l'oll~. the volumes arc too largo for lots 1 and 6. Itil'\ therefore conduded that the sharp rising asymptote occuring at thehighest mercury pressures eithor elastically and/or inelastically con­:-Itrh'ts thl' hiad, powdl'f grain. For thi~ rens~n. the mercury intrusiondata is :-Ill:-lpl'l.'t Ill'yond 10,000 psi or 70 kg cm-~.

From till' Jl'll:-lity Inl'aSllremcntfi. hoth estimates of free volume nrc~h~Hm a~ a t\m~t iOll of flame sproull rate in Figure 20. The bettor cor­rdat illll i ~ given hy the l'thN displacement volume rcflecting the volumea\"'l:l'~sihll' from olltsiJl~ the grain.

If tlt<.' vn!lIl111' oCl..'upic.1 hy moisture is considered, then it is clearthat a ~lIlall pel'l:.cntaA<.' of water could be significant in relation to theIlll'aslll'l'd free volume of black powder. This could bQ the physical effectuf \\'atcr on burn inA rilte. SIIulman25 and Plessinger7 have measured the"ffc~t of water on burning rate and their data is reproduced in Figure~l. Sinl:c there coulu he a difference in equipment. these data setsshl.Hlhl he examineJ Inucpendcntly. but in either ca!'>e the trend is clearanJ it is su~gestoJ here, hased on inference alone. that water plugs and~Jc~upi os passageways to reLtrd bur1ling rate.

v. rUTlIRE PLANS

'fhe ~lI~g~stion is made that for future work a density ranie andvoliltile ~olltcnt for d\ur4.:oal be established. Also. compaction pressuretor mnUnA hlacK powder shclIhl be selected atd it is proposed that surfac:llar"(l and pOl'u:dty measur('mt~J\t~ guide this study. In selectin~ compact ionpr(,~:;lIrl~, die JimC'n~i.on~ ~h:)llld be considered and the density distribution11ctt'rmineJ. 'Il1(' Jellsi t}' of blad powder is un indirect met! '~utc of gros!'\~tructuru being ~en6itiv~ to the density of charcoal and particle sizenf ingn'dicnto.;. From prc:'ient work. it is proposed that the internal:-Itructlll'C be m(lU$UreU and controlled. In such a study it is proposedto ~C'nL'rat(' 1I stllndnrJ meal and form black powder ~3mples t!lat providt.a ~rentur variation in uen~ity. porosity and surfa~e area to betteruocument the effoct of th~se v~riable5.

47

I!

I1

I!

..... '"'1 •••___.."",,",,",,,,,~~___.,.......... ,..---...~.~,,,,_---"," '~_~T_

,\ !jiI

0•·•• .. ...

C• ~...

C00 U-fl'i ~~~.. ...III....

• a..-g

/1'1.. - 01

!! Ii....~I..

'" CI'

~C

0 ....• - . cN ~I - .ai• .. c

~~

.. !~~

· C-....~ .&:

IIICI + .. 0....r+-II

-~toI -I ~- 0::

r+ -N$l- · ~

~~+++ l:'l....+ + · LI.

* ·I ••I • I . . • • . 0

0 0 0N -. \ .

C"')" 'e,l(Iua) iWI.L £)NIN~ne

48

.. - ,.....--_;..~

VI. SUMMARY

1. It was found that compaction of black powder meal produces con­siderable plastic flow and forms a conglomerate matrix of interconnectingpassageways to the cxtent that the internal free volume is but a few)1l'fl'ent.

~. Corrt'lations between intcrnal surface area. porc volumc. and~knsity Wt're madl' with burning rate.

3. It was suggested that thc adverse effect of water is the resultof occupying the free volume of black powder and retarding burning rate •

..\. From the ahove rdationships and S.E.M. microphotographs thehypothesis was t'stabl isht'd that an increase in the degree of openness ofIliad:. pO\~der gra i ns increases burning rate.

ACKNOWLEL>GEMENTS

:\%istanl'l.' from several peoplc was required to complete this study.Till' Iwlp and l'Ol'IH.'ration recl'ivcd was gratifyin&. I also drew extc,-sivdy llpon Kl'vin Whitt"s lABB) experience with black powuer; his cO..lnseland advil'e arl' a hallmark of this study. Other credit is given in thete.\t \\·hl.'I'I.' appl'opriatl.'; however I would like to mention here thoseindividuals who assisted in this work: Ralph Benck (PMB). Dominicl1i Berardo lP~IB) •.John Gavel (Dupont). Gould Gibbons. Jr. lEEB). LleanoroKayser lNSW). Dnd Jean Owens (Micromeritics). Perspective was gained byl'onversations with lIugh Kerr lGOEX. Inc.) and lIugh Fitler (lCIA) and Ithank hath men for allowing me to tour their facilities. I also expressmy appreciation to Eli Freedman (ABB) for his translation of part of aFl'C'nl:h reference whidl is given as an appendix. I also thank Lois Smithfor helping preparp this manuscript.

1.

,-.

.t •

s.

...

8.

9.

ll),

REFERENCES

Taucusz Urbanski, Chemistry and Technology of nxplosives, Vol 3,Pergamon Press, NY, pro 322-346, (19b7).

A.·thur Marshall, Ex.ph"'sivcs, Sec. Ed. Vol 1, lIistory and Manufacture,r. Blaki~ton's Son and Co., Philadelphia, (1917).

130 T. Fedoroff and O. E. Sheffield, Encyclopedia of Explosives andI{dated Items, Vol 2., PATR 2700, Pieahnny Arsenal, Dover, NJ,p. BlbS-B17K (19b2).

Arthur P. Van~cldcr nnd lIugo Schutter, LUstor)' of the ExplosiveInd\l~tl'Y in AIII('rica, NY Columbia University Press, NY (1927).

eh.·omalloy Corporation, "A StuJy of Modernized Techniques for theManllfa~.. t\ll'(' of Black Powder", Propcllex Chemical Division, FinalR('port No. nAI-23-072-501-0RD-P-43, Jan 60, Chromalloy Corp., IL.

II. E. Carlton, B. B. Bohrer, and II. Nack, "Battelle Memorial Insti­tlltl' Fi na 1 Report on Advisory Services on Conceptual Design and11('\,(' lopm('nt of New and Improved Processes for the Manufacture ofIHad POWJl'l''', Olin Corporation, Indiana Army Ammunition Plant, 20Oct 1970, Charlestown, IN.

,J.IL Pll'ssinger and L. W. Braniff, "Final Report on Development ofImproved Process for the Maunfacture of Black Powder", Res AMURE­109, Olin Corporation, Indiana Army Ammunition Plant, 31 Dec 1971,Charlestown, IN.

Indiana Ammunition Plant, "Black Powder Manufacturing Facility",Vol. 1 and 2, Indiana Army Ammunition Plant, 1975, Charlestown, IN .

..Kjc11 Lovo1d, U.S. Patent No. 3660546, "Process for the preparationof Black Powder", 2 May 1972.

J. Craig Allen, "The Adequacy of Military Specifica.tion MIL-P-223Bto Assure Functionally Reliable Black Powder", Report No. ASRSD-QA­A-P-6lJ, Ammunition Systems Reliability and Safety Oiv, ProductAs~urance [lirectorate, June 1974, Picatinny Arsenal, Dover, NJ.

11. II. William Voigt, Jr., Pell W. Lawrence and Jean P. Picard, "Processfor Preparing Modified Black Powder P~l1ets", U. S. Patent, 3937771,Feh 10, 1976, sec also H. W. Voigt and D. S. Downs, "Simplified 1'1'0­

~c55ing of Black Powder and Pyrotechnical Igniter Pills IncludingLow Residue Versions", Seventeenth International Pyrotec::n~cs Seminar\'01. 2, ITT Research Inst., Chicago, I L, July 1980.

12. J. C. Allen, "Concept Scope of Work For MM&TE Project 57b4303Acceptance of Continuously Produced Black Powder", Report No. SARPA­QA-X-10, November 1975, Picatinny Arsenal Dover, ~IJ.

51

REFERENCES (Continued)

13. K. J. White, H. E. Holmes, J. R. Kelso Jr., A. W. Horst, and 1. W.May, "tgnition Train and Laboratory Testing of Black Powder",ARRADCOM-BRL Report No. IMR-b42, April 1979, APG, MD. See alsoI":' J. White, H. ll. 1I01mes, and J. R. Kelso, "Effect of Black PowderCombust ion on High and Low Pressure Igniter Systums", 16th JANNAFCombustion Meeting, CPtA Publication 308, Ilec 1979.

14. L. Shulman, private communication, (data quoted in reference 13),15 Jan 1978, Picatlnny Arsenal, Dover, NJ.

15. llugh Fitler, private communication - Ilraft repor~, "Acceptance ofContinuously Produced Black Powder", 8 March 1979, ICI America Corp.,Charlestown, tN.

lb. Nt-ule A. Messina, Larry S. Ingram and Martin Summerfield, "BlackPowder Quality Assurance Flame Spread Tester", Dec 1978, PrincetonCombustion Laboratories, Inc., Princeton, NJ.

17. R. A. Noble and R. Abel, Phil. Trans.~~~ London, Serios AVol. 105, 49-155, (1875).------

18. R. A. Noble and R. Abel, Phil. irans. Roy. ~, London, Series A203-279 (1880).

19. F. A. Williams, "The Role of Black Powder in Propelling Charges",Picatinny Arsenal Tech. Report No. 4770, May 1975, PicatinnyArsenal, Dover, NJ.

20.

21.

22.

.,­.. .:I.

James E. Rose, "Investigation on Black Powder and Charcoal", IHTR­433, Sept. 1975, Naval Ordnance Station, Indian Head, MD.

James E. Rose, "Black Powder - A Modern Commentary", Proc. of the10th Symposium on Explosives and Pyrotechnics, 14-16, 1979, FranklinResearch Inst. Philadelphia, Pa.

Abraham D. Kirshenbaum, Thermochimica, 18, 113, (1977).

J. D. Blackwood and F. P. Bowden, Proc. Roy. Soc., London, A213,285, (1952). ----

·i :4. Woldemar Hintze, Explosivstoffe, 2, 41, (1968).

25. L. Shulman, C. Lenchtiz, L. Bottei, R. Young and P. Casiano, "AnAnalysis of the Role of Moisture, Grain Size, and Surface Glaze onthe Combusiton and Functioning of Black Powder", Picatinny ArsenalReport No. 75-FR-G-B-15, Oct. 1975, Picatinny Arsenal, Dover, NJ.

26. L. ShUlman, R. Young, E. Hayes and C. Lenchitz, "The Ignition

52

•...- ...,~...... , ...-.-.••0'lJIi

1 •"

REFERENCES (Continued)

Characteristics of Black Powder", Picatinny Arsenal TechnicalReport No. 1805, Sept, 1967, Picatinny Arsenal, Dover, NJ.

~7. Clyde Orr Jr., Powder Technol., 3, 117 (1~6~/lY70).

2S. Arthur W. Mamson, Phpical Chemistry of Surfaces, 2nd Ed., Inter­~cicn\.'c, NY, pp. 54h-54Y (lYb7).

2~). L Alison Floou, Ed., The Solid-Gas Interfacc, Vol. 1, Marcel Ilekker11\\.'., NY, (lYb7).

~ll. IL M. ~k Into~h and A. P. Stuart, Can. J. Res., B24, 124 (1946).

:;1. Memorial Des Poudl'c~ lit Salpetres, VoL 6, Chapter fI or M. Vieillc,Gallth icr-Va lIars Et Fils, Imprimeurs-Libraires, Purls, Pl'. 256-391,llS9:;).

~2. Naval Ordnance Laboratory, Ordnance Explosive Train Designcrs lIund­hook, NOLR 1111, April 1952, Naval Ordnance Laboratory, White Ouk,~

.'.'. Robert C. Weast, ed., Handbook of Chemistry and Physics, 51st Ed ..The Chemical Rubber Co., Cleveland, Ohio, (1970-1971) .

.i,l. A. A. Shidlovskii, "Principles of Pyrotechnics", Air Force SystemsCommand, Report No. AO-A001859, 23 Oct 1974, Wright Patterson AFB,011, Translation of Izd Vo Masimostroyeniye, Osnovy Pirotekhniki,:;rd Ed., Moscow (1964).

.'~~."--

I\

APPENDIXPARTIAL TRANSLATION OF VIELLE ARTICLE~REFERENCE 30 PAGES 306~325

by Eli Freedman

II. First Series--Agglomeration of Pulverized Materials

Wl' have used the materials of RWP brown powder. ';'hose materials,lotround and sieved throllgh a silk gauze, were agglomerated dry by comprcs­~ion with n hydru01ic press, using the steel mold already doscribed.

We thus obtained pustilles of 20~mm diamel.'r, about 3.5 mm high; andblocks of triple weight, 10.5 mm high. Six pastilles or 2 blocks of thesame density constituted a charge of loading density 0.6; 3 pastilles or1 bl.:lI:k pcrmittc~l the I:,ll'l'ying out of comparative experiments at a loading

..I\.'n~ i ty of ().:;.

The sectIons of the pistons used for the measurement of pressurewere configured in n way to furnish similar crushings so as to make thetracings comparable: n piston of 0.5 cm2 for the density 0.6, and theo~e of 1.33 cm2 for the density of 0.3.

The crushings were carried to 3.5 mm and 4 mm by the use of coppercylinders s'.mi1ur to the regulation cylinders. but with a partially~

reduced cr'Jss sect ion, ratio of similitude 1/12.

Table 11, gives the results of the tests (only one half of thetable is reproduced here given as illustration).·

TABLE 11

Dens! ty

Duration of CombustionDensity of Density of

Thickness Loading 0.6 ~ng 0.3

1. 9221. 7851. 7601.7241.635

10.4411. 1911. 4711.6512.09

98.0787.1348.3317.365.22

125.0108.80

74.5728.7812.01

l' ';

f~....... -.. ,

The results of these 3 determinations are represented in Figure 15(of text), whose abscissas represent the real densities of the pastille5,and the ordina~cs, the durations of combustion. [Curve reproduced illSnsse's text as Figure 2].*

143~aaket8 ena!oS6 t~n8tato~'s oomments ~~ notes.

55

......... -

"". ". ::,. ~- -'~""""-'--"" .. - ...."i..... :.'~ •

'.

These four curves have a common shape. At low densities up to avalue of about 1.720, the duration of combustion is effectively inde­pendent of thickness whether the combustion occurs at a charge densityof 0.3 under a maximum pressure of 1200 kg, or at a charge density of0.6 under a pressure reaching 3000 kg. Itowever, combustion time slowlyincreases up to four times the combustion time of elementary dust; then,suddenly, between densitie, of 1.720 and 1.800, the influence of thicknesssuddenly manifests itself and the combustion duration increases withextreme rapidity. tending to the limits characteristic of the compactmaterials; i.e., effectively proportional to the thicknesses.

This ~ffect of compression is hardly uniquo to brown powders. Thesam~ functioning is observed with black powder materials reduced to theIlowdered state.

V. General Mode of Action of Compression

In summary, for all of the materials that we have reviewed here,the influence of compression on the duration of combustion occurs in anidentical way.

Four regimes of compressinn can b~ distinguished which correspondto four very different cumbustion modes.

In the first regime, with the weakest compression, the combu~tion

duration of the materials does not differ from that of the elements whichcompose it pZaced ne~t to each othe~. It is consequently independent ofthickness.

In the second compression regime, the combustion duration pro­gressively rises up to values reaching 4 or 5 times those that corre-spond to the grains of elementary dust, but this duration neverthelessremains indepenuent of the thickness. It i.s this type ofmateztia't thatno~ZZy oonsti.tutes the b'taok o~ b~own powde~8 actua't'ty used by artiZZe~y.

The third regime is characterized by an extraordinarily rapidvariation of combustion duration with density; the influence of thick~ess

appears and is accentuated more and more. This type of lolaterial issometimes introduced during manufacture, when compression is required toachieve excessive slowing-up of the duration of combustion of theelementary grain; but the extreme irregularity of the products does notnormally permit these types of materials to be used.

In the fourth regime, the materjals, now virtually comp~ct, showdurations of combustion slowly increasing with density and proportionalto their thicknesses.

This succession of phenomena can be very simply explained, based onthe known laws of gas flows through capillary orifices. It is known that

56

....-_ .._..... "_..._----------if 1..".,1-_4 'I.;'.@" I Ai"

\ ;

·the discharge, Q. of fluids across capillary canals of all kinds is givenby expressions of the type of Poisuille's law,

where n = diameter; P, pressure; L, length; and K, a coefficent charac­teri~tic of the ~luid; and that consequently, the flow velocities, pro­portional to Q!n-. deaease with extreme rapidity with the dimension ofthe orifices.

It is ~on~civablc that in the phenomenon of the penetration ofincandc:;\.'cnt (flamingJ gas across a heterogeneous mass, the intersticesof a ~\.'rtain orlll'r of magnitude. which will be called the first order,alont' play an l'ffcctive role; the orifices of lower or.der, e.g., 10 timesles~, permit the flamc to propagate only with a velocity IOU times less.

In relation to the above ideas consider the material formed by agglo­meration of grains at the lowest degree of compression. A system of inter­~tices exists in the charge which assures flame spreading to all of thegrain~ without a noticeable delay, or at least for a time duration negli­gible with respect to the combustion time of the grains themselves. Thismode of combustion is made evident in the numerous examples given abov~,

showing the identity of the durations of combustion of the free grainwith the weakly-compressed blocks. This is the first phase of compressionat work.

Under ~tronger compression the int.erstices are reduced by a sort oftangling of the grains, whose surfaces in contact become married in amore and n.~re complete way while blocking or reducing to a very smalldimension the entire grid of primitive interstices.

There results a new system of canals, whose dimensions remain ofthe origln~l order; rather th1n limiting on the average each elementarygrain, as in the primitive state, they limit a polyhedral kernel formedby the parti~l agglomeration of se~eral grains; and it is readily con­ceivable t'lat the average duration of combustion of these kp.rnels canvary continuously wit~ compression up to values double, triple, etc.,the duration of combustion of the pri~ .e grains without, however, aresidual sy:;tcm of first-order canals ~easing to exist in the mass, thusassuring a combu~tion duration independent of the external dimension ofthe grain. This is the working of the second phase of compression.

Under increasing compression, the numbel' of first-order canals isreduced enough 50 that the dimension of the kernels which they limitbecome of the order of a milled grain. One falls therefore into theirre~ularitics which we have observed in the third phase of compressionof the raw materials forming the grains at the moment where the influenceof thickness is starting to be noticed. These irreiularities continue

57

........... "

until all of the first-order canals have disappeared and the influenceof thickness definitely shows up.

The fourth phase of compression starts at this moment. The materialsapproach the limiting state corresponding to a porfect continuum and thevelocities of combustion vary only very slowly with density. It is infact conceivable that this velocity results from the conductibility ofthe materials for the heat accruing from a .t~ v.tooity of inttt~tion

of gtowing ga, aoro,. the second-order interstices, whose dimensions areprogressively reduced. Prom there on, there i~ a slow decrease of com­bustion velocity, while the density rises up to the practically realiziblelimits.

VI. Influence of Pressure on the Duration of ~ombustion

The results in Tables XI, XII, and XIII relating to the influenceof compression on the mode of combustion of the pulverized raw materialspermit the deduction of several qualitative conclusions about the influ­ence that pressure exerts on combustion velocity.

If one considers materials of density greater than 1.780, for whichthe proportionality of the duration of combustion to thickness is effec­tively realized, i.e., the materials that functi.on as compact, one ob­tains the following numbers [in the table] for the ratio of the durationsof combustion of the same elements to the charge densities 0.3 and 0.6(maximum pressures 3200 and 1300 kg).

The general average of these numbers is about 1.25, and the exponentof the pressure that takes account of this variation of the duration ofcombustion is about 0.25. This value was previously noted in Chap. II,as resulting from the comparison of the durations of combustion of com­pacted materials of 30/40 powder burning at densities 0.3 and 0.6.

When one considers materials of density less than 1.780, the ratiorises rapidly and attains values greater than 2.00. Whatever the errorswhich lead to irregularities in the ratios obtained in some of the pairsof experiments, we can certainly conclude that the influence of pressureincreases significantly when the compactness of the materials diminishes.The ratio 2.5 effectively recapitulat~s the proportionality of thedurations of combustion to pressures.

The discrepancy of the pressure exponents given by experimenters torepresent the influence of pressure on the combustion velocity is easilyexplained by the variable nature of the raw materials on which theyworked.

In any case, it is evident that this effect of pressure cannot be,a priori, regarded as identical for powders of different factories, andthat it is important to determine it for each particular case.

(----page 325----)

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