o A

TECHNICAL REPORT ARBRL-TR-02490

STRAND BURN RATES OF BLACK POWDER TO

ONE HUNDRED ATMOSPHERES

Ronald A. Sasse' IDTIC

May 1983

US ARMY ARMAM RESEARCH AND DEVELOPMENT COMMANDBALLISTIC RESEARCH LABORATORY

ABERDEEN PROVING GROUND, MARYLAND

"~roved for psAlic releae. distributiulsimileDTJ"'"*"'"'""""'"'"" L TC "

83 05 18 054

Destroy this report when it is no longer needed.Do not return it to the originator.

Additional copies of this report may be obtainedfrom the National Technical Informat ion Sevc,U. S. Department of Commerce, Springfield, Virginia22161.

The findings in-this report are not to be construed asan official Department of the Arm.y position, unlessso desiglnated by other authorized decuamts.

Ofm.. amh"n 6 MA Rdw Or in~ two "or

UNCLASS IFIEDSECURITY CLASSIFICATION OFP THIS PAGE (Ma D41 Enlf. ____________________

REPORT DOCUMENTATION PAGE BRE INSTRUTINS O

1. REPORT NUON 12. GOVT ACCESSION NO 2. RECIPIENTS$ CATALOG NUMBER

TECHNICAL REPORT ARBRL-TR-02490 9>9/2 ''4. TITLE (and Subtitle*) 5. TYPE OF REPORT & PERIOD COVERED

STRAND BURN RATES OF BLACK POWDER TO ONE Technical ReportHUNDRED ATMOSPHERES_______________

6. PlEPFORMING ORG. REPORT NUMBER

7. IkUTHO~t(a) S. CONTRACT OR GRANT NUMBER()

RONALD A. SASGE'

S. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT, TASKAREA & WORK UNIT NUMBERS

U.S. Army Ballistic Research LaboratoryATTN: DRDAR-BLI 1L162618AH80Aberdeen Proving Ground, MD 2100511. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

US Army Armament Research & Development Command May 1983US Army Ballistic Research Laboratory (DRDAR-BLA-S) I3. NUMBER OF PAGESAberdeen Proving Ground. MD 21005 19____________14. 40NITORING AGENCY NAME & ADDRESS(if different from Controlling Office) IS. SECURITY CL.ASS. (of this report)

O WS ECAWFCARTION D WNIA AUDI NGSCHEDULE

16. DISTRIBUTION STATEMENT (of this Report)

Approved for public release; distribution unlimited

1' 17. DISTRIBUTION STATEMENT (ofth bi.atract entered in Block 20, It different haom Report)

1S. SUPPLEMENTARY NOTES

19I. KEY WORDS'I .ntinuo on towers* side It nec~sawand middentify by block number)

Black powder Strand Burn RatePropellantPhysical Properties of Black PowderBurn Rate

26. AM" ACT (Vtm~o. emrs va N neveeitnd idettifpr by block mmbs) rajBlack. powder samples were compressed into parallelepipeds of several

different densities. Strand burn rates of these samples were determined byhigh-speed cinematography at constant pressures to 100 atmospheres. The rate

cnbe represented as r - 1.72 p0 . 1 6 4 , with the regression rate, r, in

cm/eec and pressure, p, in atmosphcreu. High-speed movies, 2000 frames persecond, shoved the combustion mode, droplet-particle formation, and imagesIthat were used to derive both surface and strand burn rates.

SECUFrIY CLASSIFICATIOll OF THIS PAGE (11be Dts Entered)4

jimrTA-Q-T1PTFDnCDITY CLARICATION OF THIS PAQW116M TIGM IagTI

20. Compaction of black powder meal was found to be a linear logarithmicfunction of applied pressure, where samples of different moisture contentformed a family of parallel lines. This same functional relationship wasfound when compressing grains of black powder and copper spheres. Thissimilarity suggests the same physical processes are occurring in bothmaterials where compaction results in plastic flow among a collection ofclose packed spheres.

I

UNCLASSIFIED

SaCURITY CLASSIICATION OF THIS PAOSE(henD 0.0 E-d)

TABLE OF CONTENTS

PACE

LIST OF FIGURES ...................... . . . . ......... 5

I. INTRODUCTION ..................... t .... o ... . ...... ...... 7

II. EXPER IM ENTA L ..... .............. .. . *... . ... . .. ... .. *. 8

A. Black Powder Samples .... . .................. .8

B. Temperature Estimate ........... * ...... ... ...... .8C. Cinematography ..... ....... f ..... ....... 0 ..... .8

III, RESULTS AND DISCUSSION ........... ... . . ........ o9

A. Compressing Black Powder Meal ..................... 9

B. Compressing Class One Black Powder Grains ......... 11

C. Atmospheric Surface Burn Rates ................... 13

D. Atmospheric Strand Burning Rates................15

E. Thermocouple Measurements .......................... 17

F. High-Pressure Strand Burn Rates .................. 19

IV. GENERAL COMMENTS ....................... * ...... ..... ....21

V. CONCLUSIONS ..................... .... ..... .. .. .. .... 24

ACKNOWLEDGEMEN TS ........................ o..........o..... 2 5

REFERENCES ....................... o ............ ... 26

D ISTR IBUT ION LIST ..................................... ... 29

AeogSoton Fa-oFTIS C"A&I,a C TAS

• ' o |By-

DiStribultion/_

Avallability Codes_C.. Avail awnd/orIDist special

3

Ii

LIST OF FIGURES

FIGURE PAGE

1. The Effect of Pressure on Black Powder HMeal............ 10

2. The Effect of Pressure on Copper Spheres ofDifferent Diameters................................11

3. The Effect of Pressure on Class One Black

Powder Graius .......................................... 12

4. Combustion Rate as a Function of Density ............... 13

5. Relative Density as a Function of Distance alonga Black Powder Strand..**.......................... 14

6. Strand Burn Rates at Atmospheric Pressure as

a Function of Density ...... &.... ........

7. Enlarged Picture of 16-mm High-Speed Film ShowingBurning Black Powder........................

8. Large Particle Size Distribution ....................... 17

9. Temperature of Thermocouple in Burning BlackPowder as a Function of Time............................d

10. Strand Burn Rates ot High Pressures ............. ..... 19

I

I

ii

5 Ua M g.ia ;~

JMMMK yU. . .. _. 5_.a . "

I. INTRODUCTION

The study of the physical properties of black powder and their influenceon combustion has been a subject for continuing inquiry at the BallisticResearch Laboratory. One report on this subject was publishe4 ip theproceedings of the Seventh International Pyrotechnics Seminar.Aa,b In thisearlier study black powder grains, prepared by the Army Ammunition Pilot Plantat Charlestown, IN, were evaluated and various physical properties wererelated to flame spread rates. It was concluded that the manufacturingprocedure of compacting black powder meal produced considerable local plasticflow among particles, forming a conglomerate matrix of interconnectingpasageways. Correlations between internal surface area, pore volume, anddensity were made with flame spread rates. These relationships and scanningelectron microscopy, S.E.M., photographs, suggested that increasing the degreeof openness of black powder grains increased burning rates.

In the present study, 2ab laboratory samples were compressed to provide alarger distribution of densities than had been previously available. Also,samples were prepared from a single batch of black powder meal, so that all

samples were chemically identical. This approach insured that any observeddifference in burning rate could be directly related to the degree of openness,f the black powder grains. Samples were pressed into parallelepipeds,burned, and photographed. Because of this simple geometry, strand burn ratescould be determined and related to densities. This is in contrast to earlierwork in which flame spread rates among a collection of grains were related tovarious measurements of free volume.

Strands were burned and photographed using high-speed cinematography.From the images, burning rates were measured from atmospheric pressure to 100atmospheres. These movies also show other combustion phemonena, includingparticle-droplet size and velocity. In the course of this research, thedensity of black powder was related to compaction pressure in the presence a-.dabsence of moisture. From these experiments, a detailed description of blackpowder evolved that should aid both the ballistician and manufacturer.

a. R.A. Sasse', "Te Influence of Physical Properties of Black

Powder on Burning Rate," Seventh International Pyrotechnics Seminar,Vol. 2, p. 536, lIT Research Institute, Chicago, IL, July 1980.b. R.A. Sasse', "The Influence of Physical Properties on BlackPowder Combustion," AR BRL-TR-02308, Ballistic Research Laboratory, USAARRADCOM, Aberdeen Proving Growid, MD, Ma*rch 1981 (AD A100273).

a. R.A. 52sae', "Strand Burn Pates of Black Powder to One Hundred

Atmospheres," Eighth International Pyrotechnics Seminar, p. 588, IITResearch Institute, Chicago, IL, July 1982.b. R.A. Sasse', "Strand Burn Rates of Black Powder to OneHundred Atmosphere," 19th JANNAP Combustion Meeting, CPIA PublicationNo. 366, Vol. I, p. 13, October 1982.

7

~~m ~ R A-ame rum

II. EXPlZR DIMNTALA. Black Powder Samples

Black powder seals wer* supplied by the U.S. Army Ansunition Plant fromits jet-mill pilot plant. Two meals were prepared; one contained maple andthe other contained oak charcoal. The material was part of the mealoriginally prepared for the "deviant lot series"* described ky Hugh Fitler3

for a project supported by the Product Asurance Directorate. Duringstorage, the meal had conglomerated to soe degree. Therefore, prior to use,it was re-ground using a mortar and pestle. Material was used which passedthrough a 120 mesh screen but not through a 200 mesh screen.

Dry meal requires a higher compaction pressure to yield a particulardensity than does moist meal. To avoid the difficulty of regulating bothwater content and compaction pressure, samples were pressed in a constantvolume die where a spacer, which limited piston travel, controlleddimensions. Parallelepipeds (4x5x22 =) were formed with a hydraulic press.This approach had the advantage of producing a series of samples ofpredictable densities by placing known weights of meal into the die. Thesamples exhibited some elaso.icity; their exact volumes and hence theirdensities were calculated f-om the measured dimensions of cach sample.

B. Temperature Estimate

Some indication of temperature and heat propagation were obtained byimbedding a bare chromel-alumel thermocouple in the middle of black powdermeal and then compressing the sample. The wires were 127 microns (0.005 in)in diameter, and they were made by the Omega Engineering Inc. of Stamford,CT. The measuring bead was three tives the thickness of the wire.

C. Cinematography

High-speed 16-mm movies were taken with a Photec IV camera made byPhotonic Systems, Inc., of Sunnyvale, CA. The camera was operated at 2000frames per second and employed a F/2.5 shutter. Either a 100-mm or 50-M lenswas fitted to a 1.4-cm extension tube. Exposures were made at F/4.5. Thesubject was about 35 cm frou the camera, and the image size was approximatelyone-quarter the size of the subject. Samples were illuminated by a 600-watttungsten lamp focused by a 455-u diameter spun aluminum paraboloidreflector. In some experiments, an Edgerton, Gerseshousen and Grier (E.G.G.)

The deviant lot series were 10 lot, of bloA powder prepared with .,alZpertubati'one in conetitutional oompaition, partile sine or depisity.

3H. Fztter, private comramiatio, draft report, "Acceptance ofContinously Pr.oduced Black Po~wder," ICI Americas Corp., Charlestown, !N,March 19?9.

4J.C. AZlen, "Scope of Work for "I 4 TE Project 5764303 Acceptance ofContinuously Produced Black Powder," Report No. SARPA-QA-X-10, PicatinnyArsenal, Dover, NJ, November 1975.

8_ _ _ _ _ _ _ _

strobe light, model FX-2, wAs used for back lighting. Ektachrome high-speedmovie film number 7242 having a 125 ASA tungsten rating was used as suppliedby Eastman Kodak O., Rochester, NY.

Above atmospheric pressure nitrogen was used to pre-presserime a windowedchamber; the cell was of similar design to that made by Kubota. In allcases, samples were ignited by a hot resistance wire.

III, RESULTS AND DISCUSSION

A. Compressing Black Powder Meal

In the manufacture of black powder, damp meal is presed into a cakeusing various compaction pressures and different moisture contents to achievea finished grain density of 1.7. The process was examined in detail bypressing meal slowly and recording the pressure and corresponding sampledensity as the pressure was increased. Samples of different moisture contentswere evaluated.

Approximately two grams of meal were accurately weighed into the die. Aknown weight of water was placed on the powder surface to provide samples to 4percent water. No mixing was attempted, and capillary action was presumed tosoak the powder. The assembly was pressed, using an Instron Corp. materialtesting instrument, model 2TDM, made in Canton, MA. The small disilacementrate of 0.254 a per minute was selected, and a load of 3,000 g/cm" (40,000psi) was applied slowly. Pressure history as a function of percentcompaction, the ratio of sample height at a particular pressure to theoriginal sample height, is given inr Figure 1. Results are given for samplescontaining 0,1,2,3, and 4 percent water, and compaction fr-nctions are gi-,en bythe set of parallel lines draun in this figure. The observed parallelismsuggests water is acting as a lubricant. The lines are not uuiformly spaced,which could reflect that the saimples did not have a uniform distribution ofwater.

The functional relationship between the logarithm of applied globalpressure and compaction was suspected to be the result of cgmpressing boundedspheres. This idea is supported by calculations of Knudsen wherb he showsthat the contact area between spheres is a linear function of porosity. Toevaluate these concepts and assess the effect of particle size, two differentsizes of nearly perfect copper spheres were individually compressed, using thesame techniques as were employed with black powder meal. These spheres wereof two diameters, 50 and 125 microns. Both diameter spheres gave the same

5N. Kubota, T.J. OhZemite,, L.H. Caveny, and M. Swumee.field, "TheMechanism of SUper-Pate Burning of CataZtaed Double Base PropeZlant.," ReportNo. AMS 1087, Dept. of Aerospace and Mechanical Sciences, PincetonUniversity, Princeton, NJ, Iftrel' 1973.

6F.P. Knudsen, J. Am. Ceramic Soc., Vol. 42, No. 8, p. 376, August 1959.

9

1000

C014

1100S10 §

0

SS

0 10 20 30 40 50 60COMPRESSION.

FIGURE 1. The Effect of Pressure on Black Powder Heal, 0, 02;6, 12; +, 22; 6, 3% and *, 4% water.

curve, which Is shown ia Figure 2. The early portion of the curve represents

the movement of material to a close packed geouetry, and the later portion ofthe curve represents plastic flow. These results suggest that differentparticle sixes do not influence grain density produced by a particularcompaction pressure. The experiment also shows that compressing uniform sizespheres results in a linear logarittmic relation of global pressure to thedegree of compaction. These coments do not address combustion where particlesize may be important. Had the compaction experiment been extended to greaterpressures, the curves in Figure 2 would approach a vertical asymptote at 65percent compaction where all voids would have been removed.

10

i

100

10Laaaa0 5 10 15 20 25 30 35 40

COMPRESSION. X

FIGUUS 2. The Zf fect of Pressure on CUpper Spheres of DifferentDiameters.

5 .2jiirVssi!5 Skase One Slack'Pouder Grains

Class one black. powder grains are about the. size of & pencil eraser; theyare smaller than 4.76 and larger than 2.38 m. They pass through a 4 but notan 6 %tasdard nook screen. Three grams of class one grains were placed In adie and compressed by the 'initron. 1fiur different smples were evaluated:1

Two ,were of fast'burning materialo Aeianc lots 10 and 11, and two were of slowburning material, deviant lots 1 eid 6. At the start of the experiment. thedie. had a loadingj density of 1.07, and aftqr cosprossion black powder cylinders

1000

r-4

10

0 10 20 30 40 50 60COMPRESSION, S

FIGURE 3. The Iffect of Pressure on Class One Black Powder Grains.

having a density of 1.74 were removed from the die. This compression processis analogous to forming delay eleiants in various inlttons. The results,given in Figure 4, exhibit the effect of global pressure on blaAk powdergrains. The four samples gave curves that can be superlposed on each other.The original densities were 1.63, 1.67, 1.86, and 1.78, but such densitydifferences do not differentiate the curves om from another. That alogarithmic function again fits the data and the data were continuous indicatethat applied pressure results in plastic flow between particles in the blackpowder grain. The experlmnt also show that the grains do not break or crushbefore they beco* coopacted. loreover, the compaction curve for these largegrains is similar to that obtained for dry meal, Figure 1; thus, this sizedifference does not affect plastic flow.

Considering the three types of compaction experiments discussed, Itappears that plastic flow is the dominant process. The functionalrelationship between the logaritbm of applied global pressure to percentcompaction seems to be the result of compressing bounded spheres as inferred

12

frost thes coppem, ezperiamts This Im relationship appears wen compressingsmall patrticle eise mea or large bla& powder graits. Considering the esedifference between black powder awl and black powder grains and the twodifferent radii of the copper Ophres, lt io suggested that the originalparticle also bee little effect an the first density resulting from applying aparticular 1global pressure.

C. Atsmsheric Surface Burn Rates

Several uninhibited black powder parallelepiped samples of differentdensities were burnied In air and photographed by high-speed cinematography.The surf acd 'burn rates were faster chan the bulk rateresulting in theevolution of a burning pyramid, the sides of which became steeper ancombustion progressad. Can pl~ins were formed normal to the burning surface,and thus four distinct gas jet* were directed outward.

hThe location of the burning front moving down the strand we. measured onsuccessive films frames, and the position histories of this interface wereplotted. Straight lines were drawN and their slopes were taken as the burnrate. Results are given in Figure 4.

7

6

5 r

I E

2

1.2 1.3 1.4 1.5 1.6 .7 1.8 1.9 2.0DENSITY, g/%:m

FIGURE 4. Combustiot Rate as a Function of Density.9burn rate of surface made by moveable piston

0 burn rate of surface made by dieo strand burn rate

13

Several ample. wave evaluated. I t mao became apparent that of the twosurf aces viewed$ Gas was burning faster than the other. It Was found that thesurface near the inveabie die face ws burning slower than the othersurf aces* A clear correlation Is shoum relating these serface burn rates todensity. for comparisons, the strand burning rates, to be discussed In thenext section, D, are also shoam in this figure.

To measure the density distribution In a ample. George Thomson and ]KsithJingo3n, of the Ballistic Modeling Division of IlL, used a 2.2 NOY protonbean produced by a Van de Greaf I accelerators The beam impinged upon a silvertarget to produce mono-energetic K edge X-rays. The analyting beam was 1.2 -iIn diaeter and tzaversed the ample In successive steps. A larger sample wasexamined than was normally prepared to emphase density differences. Resultsare shown in Figure 5 where a sharp density increase was noted as the surf acdby the moveable die face uas approached. This experimtent confirm that adensity distribution exists in laboratory press"d black powder samples * theseverity of which will depend on die dimensions sand pressing conditions.

ta .8

1.751p0 2 4 6 a 10 12 14

POSmON. MM

* Figure 5. Relative Density as a function of Distance along a Black PowderStrand. Position 0 Was the Sui fece Made by Moveable Die Pace.

14

D. Atmospheric Strand Burning Rates

Kevin White of the BlL hs performed micro-clnematography on graphitecoated class one black powder frainse and he noted that during combustion thesample burns like a cigarette. This implies graphite is an inhibitor* Sucha coating of a CR deviant lot 11 sample was measured to be 6 microns thickby S.E.M. techniques. Thus, an inhibited sample is a proper analog to classone black powder. Such samples were prepared and inhibited with a coating ofcyanoacrylate-based glue; they were burned in air and photographed. Burningrates were measured and the results are shown in Figure 6, which shows burningrates as a linear function of density for both oak and maple black powders.The standard deviation of the slope was taken as the error of measurement;these estimates are shown as error bars on the data points.

One additional experiment was performed to compare the burning rate oftwo sticks of black powder made to equal densities where one was pressed wetat low pressure and the other stick was prepared dry using higher pressures.Both samples were dried, and the burning rates were found to be equal. In

1.0

.9

E

.6

,5 ,, i p i ,

1.3 1.4 1.5 1.6 1.7 1.8 1.9DENSITY, g/cm3

FIGUR.E 6. Strand Burn Rates at Atmospheric Pressure as a Function ofDensity. 0 maple and 0 oak.

7K. White, private communication, 1978.

15

effect, the samples did not reflect their different preparation histories. Anexample of the cinematography is the reproduction of one of the 16-Mu framesin Figure 7. The picture includes the strand of black powder, ignition wire,and helical spring contacts. The flat burning surface is evident as are apreponderance of both smell and large particles. The larger particles wremeasured by Nathar. Klein of the BRL using a Quantimet 720 Image Analyzer madeby Image Analyzing Computers, Inc.

.. . . .

• S

FIGURE 1. Enlarged Picture of 16-mm High-Speed Film Showing Burning BlackPowder.

The distributions of both the length and breadth of the particles aregiven in Figure 8, and the similar distribution of these two parametersindicates that the particles are spherical and have a mean diameter of 280microns. Particle velocity was also measured, and a value of 130 cm/sec wasobtained.

The particles were collected on a fine 50 mesh screen and examined with70x stereomicroscope. They appeared as perfect smooth spheres of the variouscolors of white, black, and yellow-striped spherical bodies. In the absenceof contrary evidence, thesc spheres are suggested to be frozen droplets ofnonreactive molten black powder blown from the burning surface. In addition,

8N. Klein, "The Use of Holography in Combustion iagnostics," draftreport.

16

16

14 -

12

110aIs6 /

4

2

160 224 288 352 416 480 544 608 672 736 S00 864DROLET BREADTH AND LENGTH, MICRONS

FIGURE 8. large Particle Size Distribution. lengthand breadth.

a fine dust was collected on a polished surface and examined with S.E.M.techniques. The dust appeared as particles between 0.4 and 1.0 microns in

II size; they had sharp edges protruding from a porous irregular structure. Theyare believed to be the result of condensation of reaction products. Onlychemical analysis can verify the nature and origin of these particles.

E. riermocouple Measurements

Thermocouple temperature measurements are clearly suspect, due to variousheat losses, but an experiment was attempted to form a lower bound estimate ofhow deeply 'neat penetrated a porous sample of black powder. In a broadersense the experiment was attempted to determine if the thermocouple wouldrespond in a compressed salt matrix. The measurement was performed by placinga thin chromel-alumel thermocouple Into the center of black powder meal, andcompressing the unit. The sample was burned in air and the output signal,referrnced to an Ice-water junction, was recorded on a digital oscilloscope.Results are given in Figure 9 where zero time was arbitrarily set; also,theearly temperature, ca 1000 C, was not deemed significant. During combustion,at a burning rate of one cm per second, the temperature Increased to 480% in2.2 as before the thermocouple was exposed to the gas stream. This is a lowerbound estimate of the temperature of the liquid layer, and the gastemperature, represented by the vertical asymptote, could not be measured bythis type of thermocouple.

17

- - .. I--

00

400 +•1 +

4W

200 + +2W +I0 +++

100 ++ -+++++++++++

0

0 10 .20 30 40 50 60 70TILke. MS

FIGURE 9. Temperature of Theriocouple In Burning Black Powder as a

Function of Time.

The value of 480"C agrees well with the measurement made by lamchitz andHayes9of 46950"C for Ignition temperature using arc mase'techniques. Itwould appear that the small mass of this thermocouple and the large heatsource of the combustion front contribute to a fair estimate of thetemperature of the liquid layer. From the burning rate and time-temperaturerelationship, the heat penetrated about 220 microns below the combustion-gasinterface. From these relationships the thermocouple appears too thick tomake an accurate or even fair measurement of the depth of the heat penetration,but the experiment establishes that the heated zone is thin and smaller than220 microns.

PC. Leiihitx and Sf. May*&, 18th JANNAP Cbmbustion Witting, CPIA NublioationNo. $08, VoZ. 5, p. 169, Deoeembe 1979.

18

F. Hixh-Prapsure Strand Burn 2ates

Inhibited maple black powder samples were burned and photographed in awindowed chamber In an atmosphere of flowing nitrogen. Pairs of samples, oneof high density and the other of low density, were evaluated at severaldifferent pressures to 100 atmospheres. To reduce the obscuration effects ofsmoke, the optical, path inside the chamber was reduced to 8 me by insertingtwo plastic spacers. Results are presented in Figure 10 and Table 1. where itis seen that only a small difference in burning rate can be ascribed todifferent density samples at a particular pressure. This close correspondence

10

E

z

.11 10 10 1000

PRESSURE, atm

j FIGURE 10. Strand Burn Rates at High Pressures. Dashed lineReference 10.

19 '

TAB LE I. HIGH-PRESSURE STRAND BURN RATES

Pressure Density Burn Pressure Density BurnRate Rate

atm g/cm 3 cm/sec atm g/cm3 cm/see

133.6 1.42 5.10 15.6 1.48 2.55

133.6 1.70 3.41 15.6 1.67 2.65

103.7 1.91 3.50 14.6 1.8s 2.42

104.4 1.65 3.33 11.2 1.66 2.51

69.0 1.64 3.63 4.40 1.67 2.32

62.2 1.55 3.82 4.40 1.83 1.94

47.3 1.70 3.75 4.40 1.64 2.32

35.0 1.68 3.18 1.00 1.88 0.733

35.0 1.85 2.84 1.00 1.55 0.768

was noted over the entire pressure range. The data contain some acatter andvalues are compared to the everag oresponse curve derived from several Rsianreferences sumarizad b Williams using th data of Belyaev and Maxnev;Glaskova and TereshkIN, and Belyaev et al.'3 The excellent agreement amongthe various studies is surprising, considering that different charcoals anddifferent preparation procedures mere used. In -fact, one reason forundertaking strand burn rate measurements was to relate results to samplesthat ere described in as such detail as possible. The burn rate function, ormore precisely, the sample regression rate, r, (cm/sec) and pressure, p,

0 F.A. WZliame, AIAA JounaZ, VoZ. 14, No. 5, p. 367, MIy 1976.

1 1 A.F. B.Zyaev and S.F. Maxnev, "Dependence of Biurning Rate of 9ioks-FomingPo,,er on Pfeeur," WkZ. Alkad. Nauk SSSR, Vol. 131, p. 887, 1960.

2 A.P. Glaakova and I.A. Tereehkin, "Relation Betwn Preeaure and Bu'ning

Velocity of fEptoeivee," Zhur, Fix. him., Vol. 35, pp. 1622-1628, 1961.

13 A.F. Belyaev, A.I. Xorotkov, A.K. PFrufenov and A.A. Suiimov, "TheBurning late of Some Explosive Substancee and Mixtures at Very HighPree e,". han.. PirA. Xhim., Vol. 37, p. 150, 1963.

20

(atm), was evaluated for pressures between 3 to 100 atmospheres. Therelationship

r - 1.72 p (0.164 * 0.017) (1)wis obtained.

The burn rate curves of this and other referenced work exhibit a sharpchange in slope at pressures of a few atmospheres. Cinematography was used tosee if a different mode of combustion, such as deconsolidation, was associatedwith this transition, and no change was observed. The only difference notedwas that at low pressure the cell had a carbonaceous deposit on the chamber

walls, whereas in high-pressure experiments large droplets were observed.However, the films all looked much alike.

These burning rates were compared by K. White 14 to the closed bomb dataof Price,and an extensive discussion evolved suggesting that burn rateequations derived from closed bomb experiments are different from strandburning rate equations. Such differences were suggested to originate fromeither grain breAkup or porous burning. Presently we are investigating thisphenomenon further by burning single strands in either a small rocket motor ora closed bomb. Preliminary results give the same burning rates as reported inTable 1, indicating that porous burning or deconsolidation is not occurring.By induction, the data discussed by K. White appear to be the result of grainbreakup, and future work ohould be directed to document such effects.

IV. GENERAL COMMENTS

Several experiments have been presented to describe the compactionprocess in term of plastic flow and the overall effect of compaction in termsof density and its corresponding burning rate. Strand and surface burningrates have been shown to be functions of density; however, the dependency issmall, about 20 percent. Such differences are greatly amplified in grain-to-grain flame spread rates that can vary over this density range by 200 percentas do relatixe quickness values. Such differences have been previouslypointed out, but it is this difference that may be closely related withdevice performance. The density of black po%.,!cr has been used as a variableto relate various parayeters discussed in this report. However, as pointedout in an earlier work, , this quantity is another view of pore volume andinternal surface area. One of the important parameters that affects thi freevolume of black powder is that lot-to-lot samples of charcoal have differentdensities, and this variance can affect the degrees of porosity of black powder(at a given density) without changing the constitutional composition ofpotassium nitrate, sulfur and charcoal. Such information is not generallyavailable from either charcoal manufacturer or black powder producer, and itwould seem advantageous to make such measurements. It is possible that theorganic content of charcoal, so often reported as affecting response, isproportional to its density. This author is guided by A. Kirshenbaum's

7K. White and R. &azeee, "Combuetion and Flame Cha,aoteristiosof Black Poder.," 18th JANNAp Combustion 9eting, CPIA Publication No. 347,Vol. 2, p. 253, Ootober 1981.

21

'- -- - - ----

comments 15 that Ignition temperature of several samples was increased asvolatiles were removed; however, these volatile-free samples' ignitiontempersturas still retaincd their original rank. Kirshenbaum suggested thatsome property beyond volatile content affects ignition temperature.

The question of "organics" in charcoal and their relative contribution tocombustion has been a subject of continuing .tudy. Not the first, but a fieexample of such work is the paper by Hintzel showing a maximum in burningrate of black powder occurs at about 301 organic content In charcoal. Thisvalue was used in duront purchasing specification since 1930, and Is part of agentleman's agreement for the tirchase of charcoal. Inclusion of thisparameter into the military specification for charcoalIs long overdue. Sucha position also appears to be supported by Robertson's paper as inferredfrom his abstract of the work. (The paper was nnt available at the time ofthis vriting[i Additionally. the importance of organics In black powder wasdemonstrated by using black powder made by the total substitution ofcharcoal by various reducible organic compounds containing hydroxyl groups.Similar burning rates to black powder were measured for several mixtures. Itappears there is nothing unique about charcoal with respect to the combustionof KNO3 mixtures.

The above discourse on "organics" promotes several additional comments onother problem areas where such thoughts are my speculations that have beensharpened over a two-year period. The girst reflections concern charcoal andcontrast the jet mill lovold process to the duPont wheel mill product.

The duPont process grinds large quantities of feed stock In mounts thatapproach 3,000 pounds. This sxngle batch processing insures a great averagingof the proper'ies of individual bags of charcoal. In the more continuoub jetmill process, such differences in the input material may become aptarent in theblack powder product. Under these circumstances it would appear prudent totest tht charcoal such that a uniform material Is employed. Some degree of:haracteria.sion covld be accomplished by aralytical tests hat would at leastbracket global properties. Some tests are listed below. Earlier in 1975,

15 A. Kirshenbau, 21 eroohim'oa Aota, Vol. 18, p. 113, 19?7.

16W. Hintze, Exlosiveto e, Vol. P, p. 47, 1968.

1 7 J. obe t on, "The Ifluenc, ,,f Charcoal in the Counbu tion of BackPowder'," RARDS, Por't Hal stead, Sevenoaka, ftgland. Pr~esented at Baeic andApplied FPyoteoh :e 'ae International Conference, ARCACHON, Frac., ctober1982.

l85. Wie and R.A. Seee', "Organic S betitutee for Charcoal in"Black Powder ' T'ype Pyrothechni, Formu*ation," 1oth JA NAF CombustionMeeting, CPIA Publication No. S66, Vol. 2, p. 305, October 1982.

22

Rose 1' made similar comeits in a short but illuminating paper on blackpowder.

Analysis of Charcoal:1. Analysis for carbon, hydrogen, oxygen2. Heat of combustion3. Percent volatiles4. True density.

Such characterization would form # baseline such that the same quality blackpowder could be produced again. More important, such data could be correlatedto functional performance And be the basis for a comprehensive militaryspecification for charcoal.

Black powder itself should also be characterized further by tests thatrecognize that "as chemistry influences combustion, so do the physicalproperties of the material." Such tests could include:

Analysis of Black Powder:1. Combustion tests (flame spread etc.)2. Performance related tests (gun)3. True and bulk densities4. Internal surface. area (B.E.T.)5. Grain size distribution.

Another area of concern is related to pressing meal to produce a blackpowder "cake." In the DuPont-GOEX press pressure is applied slowly andapplies force over a time period of 15-20 minutes such that plastic flow mayreach equilibrium or steady-state. In contrast, in the jet mill process thepress will exert force for less than one minute. In both cases a densitydistribution will occur thoughout the samples cross section, and perhaps asharper distribution will occur in the latter instance. The physicalprocesses which are both geometry and time dependent that are operative duringpressing seal are not clear. For instance, in a closed die the frictionbetween the die wall and sample will lead to a density distribution. Thiseffect will lead to a redistribution of water within the sample whichcompounds density differences. Dynamic effects could further enhance theproblem. Even in the many large, 720 X 24 X I inch, thick slabs made by GOEX.a small density distribution is observed, and this difference is induced evenin a large open sided die where pressing is done in three incremental stepsas more meal is added. The total problem of distribution appears too complexfor analysis and it would be better to measure the density distribution of a

19J.E. Roae, "Investigation on Black Powder and Carooal," IHTR-433,Sept ember 1975, Naval (rdance Station, Indian Head, MD, October 1982.

20L.O. Burohett, "PRESS: A Computer Progra For Evaluating ExploeiveMaterial Loading Pr'oesses," Eighth international Pyroteohnio Seminar,p. 991, 1f Reear'ch Institute, Chioago, IL, July 1982.

23

"cake" produced in a particular way. If the density extreme are stgnif icaantwithin the "cake" then such differences would greatly influence combustion.

The funcional tests described should characterise both charcoal andblack powder such that different lots can be compared in relation to theirphysical as wll as chemical properties. Such data, together with performanceevaluations, could lead to more realistic military specifications. In this"general comments section" concern should be restated on a major topic ofthis paper, nmely the comparison of strand and closed bomb burn rate data.Differences in combustion rate wre speculated to originate from grain break-up and If this be true then structural-strength of black powder will be animportant parameter in understanding combustion. This type of Information isrequired to assure proper perforsance and assure sound testing procedures.These differences In burn rates should be resolved.

V. CONCLUSIONS

The object of the present work us to make a more reproducible blackpowder and to remove sow of the mysticism associated with its manufacture.Insight into compaction and how the process affected the strand burning rateat high and low pressures Is presented. The mode of combustion seemsinvariant to pressures of 100 atmospheres. Results confirm the earlierobservation that the burning rate is directly related to the degree ofopenness of a black ponder grain.

24

ACKIUDCKHNTS

Assistance froa several people f ran the BIL was required to complete thisstudy, end I thank Kevin White who has worked beside we and has been principalauthor on several black powder f lam propagat ion studies. Ell Freedman'sadvice and evaluation of the thermodynamics of black powder sybtes hasprovided Insight Into black powder system8. Severl experiments wsrGperformed by Gould Gibbous, Jr., Nathan Kl~ein, Dominick DiBerardo, Timothy

Brosseau, George Thomson add Keith Jamison.

I25

4• I

REIERINCES

1. a. R.A. Saos', "The Influence of Physical Propertios of BackPowder on Burning Rate," Seventh Internat.'onal Pyrotechnics Seminar, V31. 2,p. 536, liT Research Institute, Chicago, IL, July 1980.

b. R.A. Sassa', "The Influence of Physical Properties on Black PowderCombustion," AR BRL-TR-02308, Ballistic Research laboratory, USA ARRADC0,Aberdeen Proving Ground, AD, March 1981 (AD A100273).

2. a. R.A. Sass', "Strand Burn Rates of Black Powder to Onethindred Atwospheres," Eighth International Pyrotechnics Seminar, p. 588, IrResearch Institute, Chicago, IL, July 1982.

b. R.A. Sasse', "Strand Burn Rates of Black Powder to One HundredAtmospheres," 19th JANNNAF Combustion Meeting, CPIA Publication No. 366, Vol.I, p. 13, October 1982.

3. H. Fitler, private coemunication, draft report, "Acceptance ofContinuously Produced Black Powder," ICI Americas Corp., Charlestown, IN,March 1979.

4. J.C. Allen, "Scope of Work for MM & TE Project 5764303.Acceptance of Continuously Produced Black Powder," Report No. SARPA-QA-X-1O,Picatinny Arsenal, Dover, NJ, November 1975.

5. N. Kubota,, T.J. Ohlemiller, L.H. Ceveny, ant, M. Summerfield, "TheMechanism of Super-Rate Burning of Catalyzed Double Base Propellants," ReportNo. AlS 1087, Dept. of Aerospace and Mechanical Sciences, PrincetonUniversity, Princeton, NJ, March 1973.

6. F.P. Knudsen, J. A. Ceramic Soc., Vol. 42, No. 8, p. 376, Aug. 1959.

7. K. White, private comunication, 1978.

8. N. Klein, "The Use of Holography in Combustion Diagnostics,"draft report.

9. C. Kanchitz and E. Hayes, 16th JANNAF Combustion Meeting, CPIA

Publication No. 308, Vol. 3, p. 169, December 1979.

10. F.A. Williams, AIAA Journal, Vol. 14, No. 5, p. 367, May 1976.

11. A.F. Belyaev and S.F. Maznev, "Dependence of Burning Rate of Smoke-Forming Powder on Pressure," Dokl. Akad. Nauk SSSR, Vol. 131, p. 887, 1960.

i2. A.P. Glaskova and I.A. Tereshkin, "Relation Between Pressure andBurning Velocity of Explosives," Zhur. Fla. Rhim., Vol. 35, pp. 1622-1628,1961.

13. A.F. Belyaev, A.I. Korotkov, A.K. Parfenov, and A.A. Sulimov, "TheBurning Rate of Some Explosive Substancee and Mixtures at Very HighPressures," Zhur. Fix. Rhim., Vol. 37, p. 150, 1963.

26

REFERENCES

14. K. White and R.A. Sasse', "Combustion and FlameCharacteristics of Black Powder," 18th JANNAF Combustion Meeting, CPIAPublication No. 347, Vol. 2, p. 253, October 1981.

15. A. Kirshenbaum, Therwochirica Acta, Vol. 18, p. 113, 1977.

16. W. Hintze, Explosivatoffe, Vol. 2, p. 41, 1968.

17. J. Robertson, "The Influence of Charcoal in the Combustion of BlackPowder," RARDE, Fort Halsteod, Sevenosks, England. Presented at Basic andApplied Pyrotechnic's International onfirence, ARCACHON, France, October1982.

18. S. Wise and R.A. Sasse', "Organic Substitutes for Charcoalin "Black Powder" Type Pyrotechnic Formulations," 19th JANNAF CombustionMeeting, CPIA Publication No. 366, Vol. 2, p. 305, October 1982.

19. J.E. Rose, "Investigation an Black Powder and Charcoal," IHTR-433,September 1975, Naval Ordnance Station, Indian Head, MD, October 1982.

20. L.O. Burchett, "PRESS: A Computer Progrsm for Evaluating ExplosiveMaterial loading Processes," Eighth International Pyrotechnics Seminar, p.991, lT Research Institute, Chicago, IL, July 1982.

2

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