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TITLE: THE IGNITIONPICRATE (KP)LOW-VOLTAGE ,

AUTHOR(S):

SUBMITTED

I’)

AND DEFLAGRATION OF POTASSIUMAND KP/EXPLOSIVES MIXTURES:NONPRIMARY DETONATORS

Robert H. Dhegar

To: SIXTH INTERNATIONAL PYROTECHNICSSEMINARESTES PARK, COLORADOJULY 17-21, 1978

By acceptance of this article for publication, the ‘publisher recognizes the Government's (license) rightsin anycopyright nndtheGovernment nnditsauthorized ,representatives huve unrestricted right to reproduce inwhole or in part eaid article under any copyright●eurwi by the publisher.

The Los Aiamos Scientific Laboratory requests thnt thepubiisher identify this article as work performed underthe auspices of the USERDA.

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THE IGNITION AND DEFLAGRATION OF POTASSIUM PIC~TE (KP) ANDKP/EXPLOSIVES MIXTURES: LOW-VOLTAGE, NONPRIMARY DETONATORS

by

Robert H. DinegarUniversity of California, Los Alamos Scientific Laboratory

IDS Alarnos, New Mexico

ABSTRACT

KPmmhanLcuUg blendedwtih PETN oh lfMXin 10/90%bg ma&$w“xiumu extibti h- hot-tie Lgtion behaviokto pticKP. Thue de(lagting mitititigenude tigh~ patidtiuthan ptie KPand me fitieio~emoke tie&4?a donohchakgti~ok acctiuting an .impacXptie otio an acceptoa cha.xge ok~ok hiving a ~titi~wave into a deilagtion-~o-ddondion4%an4iZioncluvlge.

lgni.l%onand de&ugmtion 06 KP and KP/explobhu mix-.t@w have been @,uLiedin 2- of Ma& dependenceon explo-hive, &edzic&, and configufuu%onpamme$wu. The.6eatitime apptiedto Xhe dev~optnetiO( detonatou 06 Iwo .tgpu, &tg-kng p.hte dtiontiou and de&agkatLon-to-de.tonu.t.ion ttamLtiondatonato~u.

I. INTRODUCTION

Potassium picrate (KP) is a high-temperature stable,crystalline substance that can be ignited to deflagrationby a rapidly heated bridgewire. The voltages and currentsnecessary are in the area of several volts and amperes.KP mixed with secondary high explosives such as PETN andHMX also can be ignited at these same levels.

The development of the deflagration in ignited KP/high explosive mixtures depends greatly upon density a~:ddegree of confinement. High-density (ca 1.6 g/cm3) mix-tures confined in thick-walled steel or brass generateda maximum pressure of around 0.3 GPa in a volume of about1 cm3, in several milliseconds.

We have not found pure KP useful in detonators. KPmixed with PETN or HMX, however, can be used as initiatorsof other explosive charges in low-voltage detonators con-taining no primary explosives.

II. KP MIXES AS DONOR CHARGES

KP mixed with PETN or HMX can be used as donor chargesin hot-wire detonators in two ways. In the first, which iscalled “deflagration-to-detonation-transition” (DDT) initia-tion, the deflagrating donor charge is coupled directly to aconfined secondary explosive charge. This transition chargemust. be of such type, density and size that the deflagrationwill change into a detonation. The second, which is called“flying-plate” (FP) initiation involves igniting ,khedonorand using the pressure generated to shear a metal disk. 1This flying plate moves across an air gap and impinges on anacceptor explosive. The accept~r explosive must be of suchtype, density and physical dimensions that it is shock in-itiated to detonation by the impacting flying plate.

A. Deflaqration-to-Detonation-Transition Initiation

Figure 1.is a diagram of the assembly used in DDT initia-tion experiments. The igniter wire is Nichrome V, usuallyO.OS-mm diameter and l-mm long. The donor charge normallyis 7.6-mm diameter and 6.8-mm long. Coupled to the donorpressing is the transition charge. Its diameter is signifi-cantly smaller than that of the donor; it is 2.5 mm. In thischarge the deflagration becon,es a detonation. An acceptorpellet is placed against the face of the transition charge.

Table I shows the resultu of a rough survey of the KP/PETN donor composition at two densities with a low-densityPETN transition charge. It appears only KP/PETN donors of

Charge

r Charge

Bridgewire

LTo Firing Unit

Figure 1 Deflagration-to-Detonation Transition (DDT) Assembly:Reduced-Diameter Transition Charge

.

TABLE I

EFFECTOF DONORCHARGECOMPOSITIONAND

LOADINGDENSITYON DDT REACTION

REDUCED-DIAMETERTRANSITIONCHARGE

TransitionCharge AcceptorCharge

PETN S: = 330 m2/kg PETN S: = 330 m2/kg

Density= 1.0 g/cm3 Density= 1.6 g/cm3

Diameter= 2.5 mm

Length= 6.4 mmIgnitionVoltage= 2.5 V

DonorCharge ResultExplosive (% by mass) Density D=Detonation

(g/cm3) ND=Ignitionbut no Detona-tion

KPt!

KP/PETN1! t!II I?

II 1!

II II

II 1!

It It

100100

90/1050/5025/7510/9090/1050/s025/7510/90

1.61.21.61.61.61.61.21.21.21.2

NDNDNDNDDDNDDDD

less than 25% KF’at high density, 1.6 g\cm3, and below 50%KP at 1.2 g\cm3, function satisfactorily.

KP\PETN 10/90 (% by mass) mix has been most extensivelyinvestigated as a donor. KP\PETN 10/90 mix, PETN, RDX, andHNAB at different densities have been used successfully asthe transition charge. High-density PETN or 9407 PBX havebeen used as the acceptor charges. The criterion for achieve-ment of detonation in the acceptor explosive was the produc-tion of a dent in a 20/24 Dural “witness” plate (18-mm thick),placed across the face of the acceptor charge. Table II showsthese data.

KP mixed with HMX also has been investigated as a donorcharge. Mixtures of composition 10/90% by mass KP/HMX, ata density of 1.6 g\cm3, have been found to ignite satisfac-torily. Table III shows the data with PETN of four differentdensities as the transitio:~ charge.

With both these donor charges there seems to be a max-imum density of the transition charge that will build up todetonation in this configuration. This is consistent withthe picture of the DDT mechanism drawn by Sulimov, where oneaspect is the combustion products penetrating through poresinto unreacted explosive, preheating the materia} and help-ing the initiation of a low-velocity detonation.

The abrupt change in diameter between the donor andtransition charges could cause the shearing effect shownby Campbell in 1976 to be necessary for the transition fromburning to detonation in the propellant FKM at high-density.3Although in our system this may be helpful, ~.tappears notto be necessary. DDT reactions have been generated withoutthis discontinuity. Figure 2 shows the assembly used withKP\PETN 10/90 mix of density 1.2 g\cm3. Here the donor andtransition charges are the same diameter with the latter ofslightly shorter length (5.0 mm vice 6.8 mm). Two detona-tions were obtained in four experiments. The two that failedappeared to be caused by incomplete burning of the donor.From these results we infer that bhe DDT that occurs with nochange in donor\transition charge diameter is marginal.Since we have no difficulty in achieving DDT when the tran-sition charge is smaller in diameter than the donor we con-clude that here there is a margin over threshold conditions.

The effect of changing the length of the dcnor chargealso has been investigated. KP\PETN 10/90 mix was the ex-plosive as both the donor and small-diameter transitioncharge. With a density of 1.2 g\cm3, the donor lengthcould not be decreased significantly below 6.8 mm. Witha donor density of 1.6 q~cm 3 its lencjt,hcould be shortened

TABLE II

EFFECTOF TRANSITIONCHARGEEXPLOSIVETYPE AND

DENSITYON D~~ REACTION

REDUCED-DIAMETERTRANSITIONCHARGE

DonorChar~e

KP/PETN= 10/90%by mass

KP S: = 250 m2/kg

PETN S: = 330 m2/kg

Donor ChargeDensity(g/cm3)

1.61.61.61.61.6

1.21.21.21.2

1.61.61.61.6

1.21.2

1.61.6

1.61.6

TransitionCharge AcceptorCharge

Diameter= 2.5mm PETNa

Length= 6.4mm Density= 1.6 g/cm3

IgnitionVoltage= 2.5 V

TransitionCharee-.

Explosive

PETNa1?1!!1It

?!ttIIf!

KP/PETN10/90!! ItIt tttl 1!

II II

!I !?

HNABdIt

RDXII

Density(g/cm3)

0.60.81.01.2~04

0.81.01.21.4

1.11.21.41.6

1.21.2

0.81.0

0.81.0

ResultD=DetonationND=NoDetonation

DDI1D and NDND

DDDND ‘

D’NDNDND

DD

DND

~pETN: Reprecipitatedfrom acetonewith Water;S: = 330 m2/kgIgnitionVoltage: 40 V

~Dent observedin Al slugused in placeof acceptorpelletpHNAB: Reprecipitatedfrom acetonewith ethylalcohol; S: = 600 m2/kg

TABLE III

EFFECTOF TRANSITIONCHARGEDENSITYON DDT REACTION

REDUCED-DIAMETERTRANSITIONCHARGE

Donor Charge TransitionCharge.KP/HMX= 10/90% by mass PETNa

KP Sp = 200 m2/kg Diameter= 2.5 mm‘P

HMx so = 350 m2/kg Length= 6.4 mm

Density= 1.6 g/cm3

●

AcceptorCharge

PETNa

Density= 1.6 g/cm3

TransitionCharge _ - Result

Density D=Detonation(g/cm3) ND=NoDetonation

0.8 Dc

1.0 Dc and NDb

1.2 NDb

;PETN: Reprecipitatedfrom acetonewith water;S: = 330 m2/kg~IgnitionVoltage= 40 VIgnitionVoltage= 3 V and 40 V

Acceptor Charge

\ fTransition

Steel~ k Donor

b

\

b

Br

Plas

)’ To Firing Unit

.

Charge

Charge

Bridgew ire

Figure 2 Deflagration-to-Detonation Transition (DDT)Assembly: Equal-Diametier Transition Charge

to slightly less than 4 mm. Failures were the result of no. .

i9nlt10n Of the donor, thought to be due to inadequate con-finement near the wire.

We have recently shown that DDT reactions will occurin pure PETN and HMX if the conditions are correct. Wefind these to be (1) high donor charge density with lowtransition charge density, and (2) a large ratio of donor-charge to transition-charge diameter. For PET?J the particlesize is relatively unimportant; for HMX a high specific-surface material is needed for adequate donor ignition.

B. Flying-Plate Initiation of Acceptor Charge

One assembly used in flying-plate initiation experimentsis shown in Figure 3. The igniter wire is again Nichrome V,0.05-mm diameter and l-mm long. The donor charge dimensionsare 7.6-mm diameter and 6.8-mm long.

As in the DDT reactions pure KP is deficient as a donorcharge. Only the thinnest of aluminum disks could be shearedand these did not initiate acceptor pellets. KP\PETN mixturesof 50/50 composition or more PETN, at loading densities1.2 glcms or above, all drove flying plates that did initiatehigh-density PETN, RDX and 9407 PBX pellets 7.6-mm diameter by5.O-mm long. These results are shown in Table IV. Onlylimited success was achieved with KP\HMX donors.

Experiments in which the aluminum flyer impacted on anacceptor charge whose diameter was reduced to 2.5 mm - thesame as the flyer diameter - were successful with both typesof donors. Data obtained using KP\HMX 10/90 mix donors attwo densities are shown in Table V. It is evident that HMXand HNAB acceptor pressings - at several loading densities -can be used to initiate large high-density 9407 PBX boosterpellets.

Bath KP\PETN and KP/H.MX 10/90 mixes will initiate small-diameter (ca 1 mm) high-density mild detonating fuse (MDF).Lead-sheathed PETN and aluminum-sheathed HNS both have beendetonated by KP\PETN-driven flying plates. PETN MDF has beenset off by KP\HMX-driven flying plates. MDF, in turn, willinitiate high-density secondary explosives.

Another flying-plate device (Figure 4) also has beenused. This design has side-entering leads. Hopefully thiswill allow additional rear confinement. The donor-chargelength is 6.2 mm in the second assembly instead of 6.8 mm.The donor diameter is the standard 7.6 mm.

Brass

Bras

Acceptor Charge

Disk; Becomesying Plate”

Donor Charge

Plastic

)’u Ehrome X Brlclgewire

To Firing Unit

,Figure 3 Flying-Plate Initiation Assembly

.“

TABLE IV

FLYING-PLATEINITIATIONOF ACCEPTOREXPLOSIVES

LARGE-DIAMETERCHARGES

Donor Charge

KP/PTN MixesBKPso= 250 m2/kg

PETN S: = 320 m2/kg

DonorCharge ThicknessKP PETN Density (mm](% by mass) (g/cm3)

90905050so5025252s10101010:010101!)1010101010101010

—

10 1.6 1.2710 1.2 1.27so 1.6 1.2750 1.6 1.27so 1.2 1.2750 1.6 1.277s 1.6 1.2775 1.2 1.277“ 1.6 1.2790 1.6 1.2790 1.6 1.2790 1.6 1.2790 1.6 1.2790 1.6 1.2790 1.2 1.2790 1.2 1.2790 1.6 1.2790. 1.6 1.279!) 1,6 1.2790 1.6 1.2790 1.6 0.6490 1.6 0.6490 1.2 1.2790 1.2 0.6490 1.6 1.27

FlyingPlate —FlyerMaterial= 6061-T6AlFlyer Barrel: Diameter= 2.5 mm. .

Length = 6.4 mm

AcceptorExplosiveDensity1.6 g/cm3

PETNVIII11!1

9407 PBXPETNIt

9407 PBXPErN!!1!t!

II

tt

It

9407 PBXIt !1II !1II !1

!! 1!

RDX

IgnitionVoltage~

404040340340403334040403~

34033333340

ResultD=DetonationND=No Detonation

NDaNDDNDa

DNDaDDNDDDDDDDDDDDNDDNDNDNDD

aDiscnot ruptured

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----- =-- .:--- .’ --- -------.... - :.’

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: ,.4

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,,,..”- . . . .

ii--:: -+-::’,,. -”:.-::,:..:~

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-. -’-. .:!--:—- . .

~-, - ---- . . .-.. ~—..

-,------

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---. .-_

----4

--

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-.. .

-.. . . . ---- ---.------ :

&.-.-:- ----- +---- .-

-,

-:, ---‘---- -

------~-

- .- -“-- ,.-

-. ----:_-. -------

-.----.

A----

b--- -. :-.:. *--- —-. . ::-: :=- -.:—- ----- ~--’---- --- :.---.--

TABLE V

FLYING-PLATEINITIATIONOF ACCEPTOREXPLOSIVES

REDUCED-DIANETERCHARGES

DonorCharge AcceptorCharge_ BoosterCharge

KP/HMX= 10/90%by mass Diameter= 2.5 mm 9407 PBX

Densities= 1.4 and 1.6 g/cm3 Length = 6.4mm Density=

KP S: = 220 m2/kg

HMx s: = 360 m2/kg IgnitionVoltage

FlyingPlate

FlyerMaterial= 6061-T6Al

FlyerThickness= 0.64 mm

Flyer Barrel: Diameter= 2.5 mm

Length = 6.4mm

AcceptorCharge

Type Sp Density

(m2Ykg) (g/cm3)

HMx 360tl 350It 36011 360

HNAB <100!I <100II <1oo

lt <100

0.8

1.0

1.2

1*4

0.8

1.0

1.2

1,4

Result

D=Detonation

D’

Do

D

D

D

D

D

n

1.6 g/cm3

= 2.5 v

Al Disk; Becomes “Flying Plate”

\ rAcceptor Charge

\ \

Steel\\

h

dSteel sv.

&’&

/

Nichrome X Bridgewire J \ Donor Charge

I

Firing Unit

Figure 4 Flying-Plate Initiation Assembly:Reinforced Back Confinement

Experiments using both KP\PETN and KP\HMX 10/90 mix donorsto drive flying plates to initiate 7.6-mm diameter by 5.O-mmlong PETN booster pellets as well as MDF have been carried outsuccessfully. These results are shown in Table VI.

TABLE VI

FLYING-PLATEINITIATIONOF PETN AND

HNS MDF ACCEPTOREXPLOSIVES

DonorCharge FlyingPlate

KP/PETNand KP/HMXMixes FlyerMaterial= 6061-T6AlDensity= 1.6 g/cm9 FlyerThickness= 1 mm

Flyer Barrel:

Acceptora Boostera IgnitionMDF Pellet Density Voltage

Explosive Type (g/cms) (v)

DonorExplosive: KP/PETN10/90Mix q= 2S0 n,2/kg

HNs PETN 1.6 40!! 9407 PBX 1.6 3

PETN PETN 1.6 40

DonorExplosive: KP/HMX10/90 Mix ~= 300 m2/kg

--- ?ETN2 pelletslong 1.3 40

HNs 9407 PEX 1.6 40t! 9407 PBX 1.6 40t! 9407 PBX 1.6 40

%DF = Lead-sheathed PETN: ID = 0.8 mm(5 grain/ft) Length= 3.8 mm

Density>1,7 g/cm3

MDF E Aluminum-sheathedHNS-11: ID = 1.2 mmLength = 1,38 mmDensity >1.7 g/cm3

Diameter= 2.5mmLength = 5.2 mm

ResultD=Detonation

D

D

D

D

D

D

D

Booster = 9407 PBX: Diameter= 7.6 mmLength = 562 mmDensitysl.6g/cmm

REFERENCES

1. V. F. Lemley, et al, “Secondary Explosive DetonatorDevice,” U.S. Patent No. 3,978,791 September 7, 1976.

2. A. A. Sulimov, et al, “On the Mechanism of Deflagration-to-Detonation Transl:ion in Gas-Permeable High Explosive”in Proceedings, 6th Symposium (International) on -Detonation, Corc:~ado, CA, 24-26 August 1976 (ONR-Dept.Navy, Arlington, VA, 1977, ACR-221) p. 250.

3. W. Campbell, Los Alamos Scientific Laboratory, personalcommunication, 1977.