,,n.

COPY NO. .

TECHNICAL REPORT 3282

RADIATION - ENHANCED SURFACE

"T A C T IV ITY O F G A M M A H M X

THOMAS C. CASTORiNA

j1 JEROME HABERMAN

ANDREW F. SMETANA

FEBRL.' .'.Y 1966

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I

Technical Report 3282

RADIATION-ENHANCED SURFACE ACTIVITY

OF GAMMA HMX

by

Thomas C. Castorino

Jerome Haberman

Andrew F. Smetana

February 1966

Distribution of this document is unlimited

AMCMS Code 5011.1 .856.01

Dept of the Army Project IC014501A32B-01

Explosives Laboratory

Feltmon Research Laboratories

Picotinny Arsenal

Dover, New Jersey

ACKNOWLEDGMENT

The authors wish to express thir thanks and appreciat ion to Mr.Victor Siele of this Laboratory for determining the many rates of thermal

decomposition of IIMX, and to W,. Augustine 0. Allen of Brookhaven

National Laboratory for his critical revie%ý of this study.

TABLE OF CONTENTS

Page

Abstract I

Introduction I

Extp-?ir-ni ., 4

Retsults and D)iscussion3

Conclusions 1

Reconintnendat ions 1

Re ferrence s

lDist ribution List 21

Tables

P fost-irradiation stability of .vamma-lM\X 14

2 Radiation-induc-d ea., evolution asý a function of surface

area of gamma-IIM\ 1.3

3 Ih'penth'ncr of suirfact- act itity of y-IIMl\ on irradiationwith various gases- lb

4 Gase;#ous prrducts from :.lM rradiatrd lai th I1,0 and NO 17

3 Thermal decomposi1t ion ratesot rHM.%\ irradiated withvarious gases 18

Fi gures

I Wfert of atisnrbate soltent sstem on stability ofparicleiz of irradaat-d and onirradiated 0l. 6 .5 y gamma

2 lidsorpt ion i sotherms of tobalt-fif gamma-irradiated llMf\ 20

31 lependenre of surface act ivity of r1lM \ on integcrateddose of gaimma radiation 21

4 Dlepntlence of surface, a' t i% itv of y-IIM\X on compositeasosprodiv t 'of gamma' radiolvi s 22

3 (jaseýous product' of C ,() gamma radiolysis; 'f v-I\ 21

ABSTRACT

"The surface activity of one-micron partici sizv ),-ortahvdro-l,3,5,7-

I etranitro-s-tetrazine ()yIIIX) is enhaw -erd by cobalt-60 gamma irradiation.

Seerf't. " a' 11ity was mwasurf(d by a raiomntri(c defternination of adsorption

of carbon- I labeled stearyl trimethyl anirnvnium bromide- (STAll) from solu-

At doses ra.'pii t fmrnn 7) to f() \lrids, the enhanced surface activityis s..hown to be. •rl'attq( II dlis,. art] the, evolutinn of composite gaseous pro-

ducts dt'rivt',I from bulk ais wt,.ll as surfac. molecules. Al.though a one-

Mrad inradialitn (of )-11%1\ in va: t.it pro, ue'-s no chang- in surface activity,suc'h an irradiation of y-Il PIX in con tart siith water vapor results in an en-

hancem nt of surface activitv that is comparable to the effect of a 13-\lrad

dose. E•Mios.ure-of -I11%\1\ to aX arid NO increases surface acti ,ity by

28'( and 42"', re sj'r'ti 'vy: irradiat ion of thfst..-samplfcs % ith one( Mrad

give's no adlditiornal enhancement.

The inc-r,.ase', rate, (of thrmnal ,f.'cnmpo.iriort is not ,fpeifi(- to radiation-

enhanced surface' actti, ity promoted by tlivatf-r vapors but i1. found to be a

function of gamma-ray interact)ion %tith bulk moe..cules as %%ell. Ilowever,

the in•creased rates of thermal drhcomposition of unirradiated samples of y-

MIIX exposed to NO and NO, are attributed s,,h.lY to thermally unstablereaction products of NO-lINt\ an:td NO,-ilIX surface addhucts.

INTRODUCTION

In the simplest ca'Se, a surfa-e io o)r mo)lcule, )f' a solid has at most

fivr-foid coordination %hil,' its subjacent neichbeir has a completed coordi-

nation numbehr of six. Trhe.interatomic list,<ne ,s, t ither between ions or

within a given molecule, are"re lat'] ic(, the l)p'evailing fracthion of the normal

coordination number for a partiroular system. From six-fold coordination

of ions %iithin the crystal to single vapor nioh'c h'es, the Na-Cl distance

depcre.a;se-s fron 2.81 to 2.51 \. In agree.iment with this observation, the-

ara.,;of surface layvers are shomn tl) he lo'i s than those of the internal

lave.rs,. V; a n'sult, th'b iending fonrs as. ,,' as the distance+s in the stur-

face layvr arte liffrent from tIhe.e,# in the interior o)f the crystal. In addi-

lion, chaniz.s in the, inh'rnm, lear t ist imrv.,i affec I the stalte, of polarizationof ion . :A(rctclinat',. dte' th,.rmial ifvratins of ioins or mnole,''ilhs in

surface layers are less harmonic and henc^' the electron density distributionsare less symmetrical than those located in bulk.

The description of the surface layer of a solid as containing ions ormolecules in a lower than normal coordination and having internuclear dis-tances different from those in the bulk of the solid doesnot in itself supply

the key to a better undirstanding of surface chemistry. The relationshipbetween reaction rates and the structure of a surface layer under stressSwntd pr•'!i 9additional information. The bulk properties of macroscopiccrystals composed of approximately 10' atoms in depth cannot be affected

drastically by differences which exist between the structure of the interiorand that of a surface layer. Hlowever, even for macrocrystals, rate phe-

nomena that are initiated in the surface are likely to be influenced by suchdifferences in spite (if the infinitesmal ratios of surface to bulk volumes.The reactivity of solids which are surface initiated is highly sensitive tochanges induced by the screening of the surface with adsorbed atoms ormolecules.

In the screrning process, an approarch to the normal coordination numberis achieved. Thetelectron clouds of the adsorbed species supply the geo-metric balance necessary for greater symmetry of electron distributionswithin the surface layer. A nascent ,;urface is under physical tension be-cause of the tendency of the atoms or molecules to assume closer packing.Adsorbed species which car improve the screening (of the solid decreasethe stateof tension by causing the surface la)-er to expand. In the drystate, the surface of nitrogen iodide is unsvmmetric al and as such is un-

stable. As a result of this surface instability the solid particles areeasily detonated and in some instances detonate spontanteou.ly. ltoAever,when a water film is deposited on its surface' nitrogen iodide becomes sta-bilized.

I melting points and phase transitions of solids can be changed bymol•-,ries which are gx4,i screeners;. Correlationshave been made of solid-state reactions with van di r 1%aals forcPe.; of various; ambient atmospheres.There'action Mg)O - FO, * SfizFeO. proceeds very slowly at a given tem-perature in a vacuum, whereas in the presence of gases the rate is geatlyaccelerated. The greater the van der Waalz for es of the physically ad-sorbed ga,.;•s (Ar, N,3 etc., (i.e., the morethe surface resembles the idealcrystal, the greater was the obseru'd reactivity of the solids.

01

The screening of surfaces possessing highly polarizable and thermo-dynamic-ally stable anions and highly polarizing cations induces changesin the mutual electronic interactions of the ions (continuous polarization).Thermodynamically, there is little difference between tlg(N,), and 1la(N,),because the energy is vested in the labile electronic structure, N,-. Butthe tendency for fIg"4 to extract an electron from N,- is much greater than

it is for Ba". The difference in behavior betweeen the transition metal

a.d alkali 'alkaline earth metal azides isbased on the ease of this con-tinuous polarization. Crystals of llg(N,), remain stable as long as thesurface is screened with water. Removal of %ater creates a less symmetri-

,al ,iar.frc fi!. ; win , th, #-,I.trnnic interar'tinn ig intro,;J.-d , I sucrh anextent that the crystal detonates. Cupric acetylide (("u(:,) detonates onheating. But if the surface symmetry is increased by partial oxidation intoCuO, the crystal d.comnposs on heating ýitlhout detonating.

The examples cited above (0P'f 2) show that the inherent differences

which exist between the structure of the "p|rfect" crystal and that of itssurface layer in ilhich the initiating proc-esses exist is indeed of chemical

significance and that reaction rates in such cases can be affected bychanges induced at the surfaces. It should be emphasized, however, that

the study of the relationship of surface propertius to bulk properties hasbeen confined primarily to inorganic systems. Little or no wc.k has beendone in relating the two properties for organics or explosives (inorganic as

well Ls organic). In fact, there isno definitepmof that such a relationshipeven exists. Knowledgeof the existence of such a relationship would help

to indicate how the condition of the surface of an explosive affects the ex-

plosive process and would also supply practical information on altering the

sensitivity of explosives.

It is conceivable that the physical and chemical propertiesof explosives

can be aitered in a desired (lirection by changes induced at the surfaces.

By controlled exposure of the surfa(e to adsorbate species it is possible toelucidate the mechanism of autocatalytic decompxosition. As another ex-ample, by using soft elec(tromagnetic radiation, it may be possible to induce

the formation of a mono-layer polymeric film on the surface of an explosive.

In the case of explosives normanlly sensitive to electrical and frictional

energies, the thr"shold of initiation may be raised to a desired level by the

deposition of a polymeric coating. The polymer (e t., polystyrene) not only

forms a protective coating by %irtue of its inertrinss, but may also stabiliLe'

the explosive by the smre enin g eff,,ct of the. high ele(tron dlens ity existing

3

between the carbon cores. In addition, such a protec'tive coaling may be

effective in reducing the electrostatic interaction between particles Such

a reduction may be desirable in the formulation of some explosives compo-

sitions.

This report describes a preliminary phase study of the relatio-iship of in-

duced changes in surface activity to the thermal decomposition of rlMX.

A radiometric solution adsorption method developed in this laboratory (Ref1) was used to indicate the changes induced at th: surface of r-IIMX by

cobalt-60 gamma radiation.

EXPER IMENT AL

Preparation of Fine Particle HMX

Gamma-IMX\ was precipitated rapidly in water as a textured pouder from

a solution of 10 g I\IX in 25 ml dim,.thyl sulfoxide (I)MSO). The precipi-

tate was immediately filtefred and washed: it was then plarced on absorbent

paper to accelerate dryine. The jxvymoqrph of I11%\ prepared in this mannerwas shoun by infrared aivd x-ravy ani se-s to be of the Rimma forrm.

The average particle size of this mate-rial kas found| by electron micros-

copy to be about 0.65 micron. t'his value is in reasonable agreement with

the particle diame-ter of 0.90 micron calculated from the observed BET sur-

face area of 2.6 m' &.

Surface Areas

Measurements were madt- by the l BT method of Io, tempe-rature (- I%6)

adsorption of N, and or Ar.

Gas Analyses

The identification or gaseous products of radiolysis was performed by

mass specrrom,-try undier a service contract with Gollob Analytical Services,

Berkeley Ileitghts, New Jersey.

Determination of Changes in Surface Activity

* (Changes~ in surfacev artivity wfere dfetermined (as a function of chang's

in saturated adsorptions of c'arbon- 11 1 abeled steatyl trimethyl ammonium

bromide (STAB) from solution) by the radiomnetric method previously r.--

ported (lef 1).

Measurement of Trapped Gases

The release-o of occl.udvd gases %%is done wi th lfllO as thi- sol'd'nt.

[Degassed l)MSO and irradiatei- samples of I INM ~iiere mixed in a closed

system affixed %si th at breaksf'al. After dissolution of the MIX,\ The scu-u

tion %%:~is frn~zen at -78' and the gas pre-ssure measured witrh a %If (:1t-od

gauige. All volutmes '% ere adjusted to Sl 1'

RESULTS AND DISCUSSION

Annealing Studies

To more effec-tiveily pry)luce and determine- chanvfws at the surface.. 1INX

of 0.65 micron 1)art if-e size %%as used for t hi. studyv. Tbif e reasonable

agreement obtaine-d bet-tNen calculated andi obser~ d part if-b size, idi -

Coles that this material is n~onporou s. Th cr#fore anv *i kora tft-T X

molecule' interact ion wvould be confinedl toc the, surfac f, of ilhe substrateý,

Since- the areia c-overed byv the sTrkli mo '**cu I e it s atu rated idsorp~tion is

less than one half the total surfac v area if [[.%I\ thof 1). Av ha ~ecn lue

that the ads. crpt ion of S All occurs by meains (if an ifini( irt eraction lie-

tween SITAB and a polar sitw. 'I hitrefore, anN ch a nkv in -u rface activity

(active sites of a polar naturei) produced by inc-iden-t radiation ould be'

mea.- i red I., the cwt-, spotid.inz ( hangt- in the strtd-sopinValues of

s~r Ali. The normal cove rage for s1T.X I ( approx imatit ly 30"ý) %% ,Aisi make i

possible to detect deviations from this .alue in eitht-r dire~ction. OqI(-I

tions to the method may be, based on the po si bi lit y of Sinte.ricig of fini,

particles of )'-IIM in the sol en t syst er of t he ad sorbato' STAB.~ The

changes producetd on the surface of t-ll l \ uld. conri\ Aldly hobe an nteahi

by c-ontact with a liquid phase. The experimont .s sumniari.m tei in l'iiptrte

1 (p) N) were condt)lued to Iet'trmc e t he % an ablv paramvters; in~iol '#d andto establish coniditilons that %wolld mninirnli.the eI# ffectls of 1111"l, %ara i~les.

*i

A number of separate samples of the STAB-solvent system in contactwith 0.65 micron rIIMX were assayed for STAB content at various time in-

tervals. The series consisted of unirradiated and irradiated IMNIX both

sets being subdivided into two portions, one of which was degassed andthe other of which wasnot. For both sets, STAll is shown to tit sorb ex-ponentially from the IIMX\ surface asa function of tirne of contact with the

adsorbate solvent. Although physical adsorption is clearly demonstrated

in both cases it is quite obvious that the surface activity of the irradiated|HMX is significantly enhanced (to the extent of displacement of the twosets of curvesby approximately 708. %ithin the range of surface acti ity

measured by this solution adsorption mnthod, there is no observabie differ-enre between the anneaiing effect of the solvent on the irradiated samples

and its effect on the control samples. Therefow, the annealing process

must he independent of the radiation effect and dependent on some other

fa( tor.

Optical microscopic meassur.m.M'tnts sho-ed that, as desop~tion takes

place with time in both s-ts, the parti|lesof y-II\X sinter from the initialsize of 0.65 micron to an equilibrated size of approximately 11) microns inthe span of 15 to 21 hours (the asmrptotic ;xortion of the curves '%hown inFig 1). Concurrent wvith thischariwe,the crystafline form of the IIM\ con-vtrts from y to fl. as sýhoun by infrar.l analyses. The desoiption of STAB.

and hence -the anne'ding process, c an Ite attributed in either set to a de-crease in the spet ific surface activity proportional to a decrease in surface

area. The increase in crystal size' corr-sjxmnds in e-ach set to a decreaseof 0.4 mg STAB desoirbed per gram of IIMX.

An apparent difference in the rate.of crystal growth exists between the

irradiated samples that were degassed and tho.se that we.re not degassed,whevreas the comparable unirradiated samples show no similar difference.

The difference in ratesof crystal crowth could be attributedto the formationof some polar surface constituents that are loosely bound and others thatare, not removed by degassing au ambient temperature. The presence of the

former has a retarding effect on therate of crystal growth, but the removal

of the latter results in a rate curve which is similar to that of the control.

Ahere the two curves are superposable during the first hour of sampleequilibration, thiese f oinpnlil atiig arl lconcurrent processes, b.come negli-

gible. The selection of a fixe.d r tiod of one hour for the equilhnration of

all samples gave reproducible data and rendered the solution adsorption

method a useful tool for comparative measurements of surface activity.

No significant post-irradiation annealing of the enhanced surface activity

of HIMX was observed wi thin a 50-day p,,riod. This stability is apparently

independent of integrated dose over the 4- to 40-Mrad range. A significantdecrease of surface activity was observed only after 96 days post-irradiation

for a sample exposed to a 16-.lrad dose. Since all measurements were madewithin a 5-day period, annealing of radiation-enhanced surface activity was

not considered as a variable.

The chemical stability of irradiated y-II.%X is illustrated in Table 1 (p

14). Both the type and quantity of the products of the radio!ysis are con-

stant and independent of post-irradiation time. Apparently, there are nosecondary gas phase or ga•s-solid phase reactions; and there is no diffusion

of any interstitial gaseous products of radiolysis to the surface within a

36-day period. In fact, only residual quantities of occluded gases are pres-ent, as will be shown !ater. Irradiated )-1I.%IX is, therefore, showi to be

stable generally in exposures to products of radiolysis as well as to the at-

mosphere over the period of time studied.

Dose-Surface Activity interrelationships

The ro 'iation-enhanced surface activity of y-tIMX was studied as a func-

tion of intpgrateddose to establish optimum conditions for a maximum ratio

of surface-to-bulk molecular interaction %ith incident gamma radiation.

Figure 2 (p 20) showsthe effect of various doses of gamma rays on ad-

sorption isotherms of STAB on IIM\. The curves are all of the same type;

but with increasing dose, the amount of adsorption risesmore ste.eply with

increasing concentration, and the eventual saturated adsorption at the

plateau is higher. This indicates that the number of ion-dipole interactions

between STAl3 and IIMX increasc, with dose. Presumably, radiolysis of

surface molecules produces groups of a more strongly polar character than

normally exist in IIMX. The surface area of the unirradiated HtMN (2.6

M',g) decreased 22_ to 2.1 m-g after 64 Mrads irradiation. But the cor-

responding specific adsorptions (unit area basis) increased from 0.65 to

1.3 mg STAB ml, respectively, or by a factor of two.

7

I

The dose dependence of saturated adsorption corresponding to radiation-enhanced surface activity is shown in Figure 3 (p 21). There isan induc-

tion period for radiation-enhanced surface activity during the first 5 Mrads.

Of particular interest is the fact that one Mrad is the maximum dose to

which rlNIX can be exposed without undergoing changes in surface acti-vity as indicated by STAB adsorption. After an irradiation period of 5

Mrads, there is a linear relationship between dose and surface activity.The "y" intercept of this line is approximately 1.9 mg STAB g KIIX.

When the surface activity is plotted versus the composite gaseous pro-

duc;s of raediolysis (Fig 4, p 2), the extrapolated linear portion of the

curve following an induction period also intercepts the ordinate axis in theregion of 1.9 mg STAB g IIMX. Apparently, integrated dose and evolved

composite gaseousproducts are related to enhanced surface activity.

When the Compton interaction of gammas with matter is taken into con-sideration, the observed int.rrelation cannot be attributed to evolved gasesderived solely from radiolyzed surface molecules. Because gas evolutionand dose are relatedto surface acti%ity in the same manner, the assumption

is made that gaseous products of radiolvsis. as derived from bulk as wellas surface molecules, are being evolvtd from approximately one-micron

H,-llMX. Urizar (Ref 3) has indicated the reverse to he the case, presum-ably for large-particle P-IIMX. Certainly, particle size would affect thedeg.'ee of gas occlusions.

To verify the above assumption, the dependence of radiation-induced gasevolution on particle size in terms of surface area, 1, is presented in

Table 2 (p 15). The difference in surface amreas of the two samplesstudied is approximately one order oif magnitude. No attempt is made to

interpret the variations of the ,lose-dept-ndi.nt ratios of the constituentgases as a function of surface area. The combined disproportional vol-umesof evolved and trapped gases are shown to be independent of surfacearea but solely dpendent upon integrate,] dose. The ratio of evolvedgases as a function of decreasing surf ce area is much greater at the lower

dose than at the higl-er dose, roughly 8 as against 3. The escape ratio(volume evolved volume trapped) of the large-surface-area IIMX is approx-imately the same for both doses. llo%#-.er. the esciape ratio of the small-

surface-area sample is very small and incr,,ases slightly from 0.1 to 0.5with increased dose.

S.

The conclusion drawn from these ratios is that the smaller the particle

size, the greater the opportunity for gases to escape freely to the surface,and the larger is the escape ratio and the more independent of integratd

dose. Based on 2.67 x 10' A' for the molecular volume of IBMX, as de-

termined by Cady (Flef .), and using a 0.65 - 0.65 - 1.64 p model corre-

sponding to 2.6 m2 ,'g, the ratio of surface to bulk molecules was calculated

to be 1`300. Apparently, for a depth of roughly 300 molecules the diffu-

sion rateof the gases ik rapid enough for their evolution to the surface to be

virtually complete soon after formation.

From 5 to 60 Mrads, the radiation-enhanced surface activity of y-IIMX, asdetermined by the saturated adsorption of STAll, is clearly a linear func-

tion of the dose-dependent evolution of composite gaseous products derivedproportionately from surface and bulk molecules. The lack of enhanced

surface activity at I Mlrad suggests that the effect occurring at larger doses

may result from the pres-nce of gaseous products of radiolysis adsorbed on

the surface of the )-1ll\X Conceivably at one Mrad the relative pressures

of the reactive gaseous products are too low for adsorption to take place

(see Fig 5, p 23). Allen (Ref 5) has shovn that a gas phase in contactwith a solid subtrate can draw excitation energy from a considerable volume

of sdid. On an organic solid like IIMX. radicals or atoms form.ed from ex-citation and decomposition of adsorbed moleculps would react with the sur-

face of the solid, producing abnormally active sites. The total dose of

one %Mrad does not by itself induce anv measurable increase in polar sites

as determined by the radiometric metht.,i. 'rherefore. any change in surface

activity observed in samples irradiated with the same dose but while in

contact with gases must be attributed to the presence of the gases.

Irradiation of HMX Gas Mixtures

To test this hypothesis, 1 -II.%M ,as irradiated wi th I NIrad in the pres-

ence of the various gases listed in TFable 3 (p 16). In the presence of

water vapor, the radiation does in fact enhance the saturated adsorption by

13'. Exposure to NP', and NO .ncreases the adsorption %ithout radiation,

by 211' and 1.'•. respectively: exposure to I %frad gives no additional en-

hancement. These r,,sults w ,iltl imply that NO, and NO undergo chemical

reactions with surface molecules of y-lI.I\ prior to irradiation and that the

surface, adductsresultin g the retrom are stable when subijcted to the 1-Mrad

dose.

I

To shed additional light on the significance of these observed changesin surface activity, mass sp'ctrometric analyses were performed on the

gaseous productsof radiolysis of the solid gas phase mixtures. The gas

-analyses are recorded in Table 4 (ip 17). Data on the NO, IBIX mixture

were not available because NO, cannot be analyzed easily with the ma,ýs

spectrometer. The ratio of major prnducts of radiolysis for 11,0 IIMX is

identical to the ratio for vacuo IIMX. The only significant difference be-

tween these two systems is in the quantities of composite gases produced

by radiolysis. The in( reased gamma interact ion si th y-i•MX in the pre..,.

ence of water is consistent with the observed surface acitvities listed in

Table 3. The number of gaseous constituents is the same for unirradiated

NO 'IIMX as for irradiated NO IIIX with the exception of minor quantities

of II,. There is aljarentlv a dark reaction b.etween NO and IIM\ that iscommon to the radiation-induuc ed reaction. The. (CO associated With this

reaction and the high ratio of N,) to N are not observ`edt for any of the other

S ySt ems.

Although radiation produces, as t function of NO pressure, *1 to 7 times

tie quantities of gases derived from the. lark react ion, the respective spe-.:ific adsorptions are the sain'. The type of polar sit's produced by the

dark andradhation-induced reactions night be the -,aaie, but their number

may differ. The 1t.' increased adsorption repre.sents, roughly. 505 cover-age of the '-IIMX surfm e area. lBe-cause of steric hindrance, this coverage

may be considered maximum for ST\II. PresuiablN, th'umrh additional polar

sites may exist, they c annot act oimomtaie any more s'Tll molecules be-cause of the already saturated conlition of the surface of the -lIMX.

Thermal Decomposition Studies

In an attempt to relate- chanrs in surface -prop-rties to bulk behavior, a

study was made of the thermal de.composition rate of th•sc- sample. of y-IIM\ showing enhanced surface, activities, as indicated in Table 3. Theresults of this study arc' shown int Table 5 (1p 18). Because the accelera-

torN rate, k,, of irradiated %t uo IIM\ is 17"5 greater than that of unirra-diated tacuo II\IX, no ,ignificance (-an be ascrib.d to the 17"5 increase ink,, of irradiated 11,0 II•M•. NO lIM, and NO, III\. Of notewonhy inter-est are the percent inflection points (if irradiate.d NO IIX\. vaocn II\I,. and

NO I.II\, which are II, A3, andl 17. r.s;pe•tcively, as, compared to 417 for

unirradiated vacuri II.\IX. The or•er of sustained ac'celeratorv period is

it)

.----

NO3'II1MX > NOI1IMX > vacuo/lIMX. Any interpretation of thisorder is un-

doubtedly complicated by the combined effects of radiation and enhancedsurface activity. That the latter effect can play a role in the thermal de-composition rate is discussed in the next paragraph.

The NO/IlMX and NO 'lIM.\ X %hi~h were not irradiated and showed en-hanced surface activi ty ( c and 28r, respectively) are representative ofchanges that have [wen induced solely and selectively at the surface.Therefore, comparison of their thermal decunmpoqition rates with that of thecontrol, unirradiated vacuo.IIMX, is considered valid. The acceleratoryrate of thermal decomposition of both these samples is 8'• greater than that

of the control and the acceleratory period is 4V shorter.

The adsorption studies have shown that one-third of the total surfacearea of tlMX is covered by the ST \13 molcule,. [he unit cell of y41MX,

according to Cady (Mpf .) and IPepinsky (Ref 6), has freely extended polar

NO, groups at each end, and NO groups %hich are somewhat shielded (via

intermolecular hydrogen bonding) on four sides. This could account for theone-third coverage by STAB since the suggested mode of adsorption forquaternary salts is an ion-dipole interaction. Similarly, the NO and NO2

vapor molecules could be interacting chiemically with the one-third of the

surface that is hydrophilic, producing thermally unstable melecular species

of the type: H-Nil2 , RCIIO, |0(•!1iOi, and RNitNO,. The presence of thesespecies on the surface in such restricted concentrations conceivably could

increase the acceleratory rate of thermal decomposition to the extent ob-served.

CONCLUSIONS

The radiation-enhanced surface activity of IIMX as determined by satu-rated adsorption of STAB from solution is a function of the dose-dependentevolution of composite gaseous products derived from both surface and bulk

molecu les.

Gamma irradiation at low doses lias been shown to interact nonspecifi-cally with v-IM\X in the presence of paramagnetic gas molecules.

II

Increases in the rate of thermal decomposition of rIIX which has been

exposed, "withou" irradiation, to NO and NO, are attributed to thermally un-stable reaction products of NO IBIX and NO, 1 IIMX surface addicts.

Although the radiometric method of STAB adsorption from solution hasserved effectively to indicate qualitatively the changes that take piace at

the surface of NIMX, it has serious inherent limitations. The water-alcoholadsorbate system as a condensed phase in contact with the adsorbate pro-duces a myriad of interactions competitive %sith the adsorbate-adsorbent

adsorption lxtential. Thiis report hats demonstrated that these complex in-

teractions have a strong annealing effect on active polar sites and that

increases in the number of polar sites within the effectively large areacover,,d by STAll are not detected.

RECOMMENDATIONS

The dark reactio)n existing between-, NO (and presumably also NO,) and

lUNIX may provy effective in inducing change-s of a permane-nt nature(chemissorption), preferably at the- surface. Another po.sible method ofaccomplishing this wonld he b• the- activation of gas molecules to theirexcited or dissociated states with electrodeless discharge in close proxim-ity to the solid phase for efficient gas-slid interactions. Theuse of2-6 ev energy electrons with half-thickness absorptions of one to twomolecular dia'-ieters could also conceivably induce chances confined tosurface molecules.

By means of a BET apparatus, surface pro~perties can be mon. preciselymeasured and quantitatively compared on a unit area basis. The systemof measuring is relatively simple. consisting of a gas phase in contact %iththe so1 id material. heats of adsorption can be obtained from multi-temperature isotherms (isosteric heats of adsorption). From adsorptions atlow relative pressures, energy site. distributions can be calculated. W, ithimmersional heats in conjunction with preadsorbtwd quantities o' water vapor,enthalpies, free energies, and entropies of ad,;orption ('an be determined(Ref 7). Such thermod namno- surface propreri its wotuld be most sensitive toinduced chan•es anti amenable to qutaltitatix, nmeasurer tnts. In this

manner surface activities (cain be more effectimelv comparetd to bulk propertiesof metastable materials.

12

REFERENCES

1. Habenuan, J. and Castorina, T. C., Anal Chem. 36, 1917-1920 (1964)

2. Weyl, W. A., "Solid Surfaces and the Gas-Solid Interface" Advances in

Chemistry Series 33, 72-85. 19§1

3. |lrizar, %1. J., Loughran, E. D., and Smith, L. C., Explosivstoffe No. 3,55-66 (1962)

4. Cady, H. H.. Larso n, A. C., and Cromer. D. T., A4ta Cryst. 16, 617 (1963)

5. Rabe, J. G. and Allen, A. 0 , J. Am. C4'.m. So,. 86, 3887 (0964)

6. Eiland, P. F. and Pepinsky. R. 1., Kristallogr. Bd 106, 273-298 (1955)

7. Chessick. J. J. and Zettlemoyer, A. C., "Advances in Catalysis," Xl,p 263-297, Academic Press (1959)

13

TABLE I

Post-irradiation stability of gamma-HMXa

Gos~oUS6 cc (Gas) STP - 10'/g HMX with Post-l rdiotion Time(Days)Pro&cts Contro•c 3 days 4 days 6 days 10 days 24 days 36 days

H, 0.004 4.3 5.0 5.9 6.0 4.0 3.3CO Z5.7 28.6 30.0 30.0 32.9 27. 1N1 0.017 365.7 375.7 10?. 1 407. 1 442.9 358.6NO 0.023 91.4 88.6 111.4 111.4- 121.4 111.1NO 60.0 60.0 72.0 72.9 75.7 72.9CO, 0.0.'1 35.7 38.6 417.1 47.1 61.1 55.7Mass 52d 0.6 0.6 0.7 0.8 0.8 0.7

Total 0.006 583.1 507.0 67-5.3 67-5.1 739. 1 629.7

it samples (a.erage particle site-O.I ) from a common batch pre-paration. evacuated

and irradiated at same time for lh hours -b lhr.

bA% d.l•prminpd by mass Sptý, trivnetr .tnily..i..

rEv•auatpr! at qame time and i,. same. mesanner a%. irradiated %ample-: analvyis p.rformed

at end of serial analys•s.

dAn organic constituent not identified (possibly cvanompn, NC-CSN).

11

0 0

0L

0

0

UU r

0C

V u0 to-U

0

130

TABLE 3

Dependence of surface activity of y-HMX on

irradiotion with various gases

Unirrodiated x-HMX Irradiated0 Y-HMX11/2 2.3 2.1 1.9 2.1 2.3 2.0 2.1

Gas HO NO NO, Vacua HAO NO NO,

1 2 1 2 1 2

Saturated 1.11 1."5r 1..1 1.11 1.23 1.30 1.37 1.12 1.57 1.14

Adsorption 1.12 1.60 1.20 1.13 1.32 1.29 1.37 1.47. 1.47- 1.22

1.15 1.16 1.2Q 1.12 1.64 1.24mg STAR g I1\IX

L11l L,33 1.32 l.4t) 1.66

Average Adsorption

unit 1b 0.50 0.71 0.64 0.5•1 0.56 0.57 0.71 0.76 0.71 0•5-7

Dose - I Mrad.

b±0.04 mg STAR unit are,.

16

m_

0~ Li

z z

00-

0d u

oi xm~ C

* U U

w .0

17

I

TABLE 5

Thermal decomposition rotes* of rHMX

irodioted with various gases

Dose, kib, mrin" kc, in Inflex

Gas Mrad 10' ' 10' Point, %

Vacuo 12.3 8.6 46.9

1.0 14.3 8.6 38.3

H,0 12.5 8.1 47.0

1.0 14.8 9.4 39.1

1.0 14.7 9.2 38.3

NO 13.3 7.8 43.4

1.0 13.8 9.0 40.7

1.0 14.1 9.8 42.0

NOS 13.2 8.5 43.8

1.0 14.0 9.7 48.6

1.0 13.8 10.1 47.7

aValues significant to ±0.2.

bAccererstory rate of chain reaction.

CDec*Y rate of first order residual HMX deconmposition reaction.

dof acceleratory and decay rates.

18

1.4

0.65,1.3 Not D•Ossed Dogossed(o)

1.2 0 Not irradiated • Not irrodioted0 Irrodiated(b) I irradioted1 b)

. I(a) O~gossed 72 hours at 25 0.62(b) Integrated dose, 16 mega rods'0.9

Il

a I

~0.8 1

0.70.

0.6

0.5

O.S • 10f,

0.4

0.3

0.2

0.1

5 10 15 20 25

Time, Hours

Fig I Effect of odsorbate solvent system on stability of particle size ofirradiated and unirradiated 0. 653L gamma HMX

19

Ow"I

r44

iii

000t -

SS

'0-C

0 ajC,.

-Cb

cinsyls w 'uiidjtpyo

MS

C

- 0 0

*3;

- -u CDa M

SO C

LL

CDali0

6,19IS O 'utidjspype~col0

4

0

0

aa -�z -: a-u aEC B E

aa'0

-u0

a.0a0

C 0oa'

0

00

Ea.N 0z

£0a

UCUCN

0

C

Ua0Ua

B- 0

C

0UC0

o C0a.0

C C S CC -, a'

XWH 6 �yj� Ow uo,�diotpy parn��

�V)

N,

2.000

I.H

8 16 24 32 40 48 56 64

0ose, mega fods

Fig 5 Gaseous products of Co" gamma rodiolysis of y-HMX

23

UNCLASSIFIED

Secunty ClassificationDOCUMENT CONTROL DATA - R&D

0aletvtte cl'a.Ifcalecn of oft, ban, of obouD and tndbt•ntEi an•a•ftl• must be afarmE sawn M o mitD? amgen tm eiaommitmdeIOF*IGIWAY TIM ACTIVITY fCofpoereo mawt) |20. ACPORT *CtCUO TY• C LA#SIWSCAT#Of

UNCLASSIFIEDPicatinny Arsenal, Dover, New Jersey 2s **Do,,

a, REPORT TITLES

RADIATION-ENIIANCED SUHFACE ACTIVITY OF GAMMA HMX

4 DESCRIPTIVE NOvaES (T. of m an . s don*v )

S AUTIOR(S) (L*Dt ma tifa ntn'm. uteD)0

Castorina, Thomas C.; IHaberman, Jerome; Smetana, Andrew F.

SREPOR T DATE Ta TOTAL NO oF E"INO OP API

Februar_ 1966 27 7Sa CONTRACT OR GRANT No. . ORIGINATOR'S REPORT NUI[SERS)

&na scr "o MCI DA 1C014501A32B-01 Technical Report 3282

M.,CMS Code 5011.11.856.01 sa :z.rR T nO) (Aryedmmamnboem tat may ba mmmssmd

It. AV .,LAUILITY/LIUITATION NOTICES

Distribution of this document is unlimited.

It SUPPILIMENTARY NOrnS IS. PONISORING MILITARY ACTIVITY

11 ABSTRACT

The surface activity of one-micron particle size y-octahydro-1,3,5,7-tcetranitro-s-tetrazine (y-HMX) isenhanced by cobalt-60 gamma irradiation. Surface activity was measured by. a radiometric determina-tion of adsorption of carbon-14 labeled stearyl trimethyl ammonium bromide (STAB) from solution.

At doses ranging from 5 to 60 Mrads, the enhanced surface activity is shown to be related to dose andthe evolution of composite gaseous products derived from bulk as well as surface molecules. Al-

though a one-Mrad irradiation of y-HMX in vacuo produces no change in surface activity, such as

irradiation of rHMX in contact with water vapor results in an enhancement of surface activity that iscomparable to the effect of 15-Mrad dose. Exposure of rHMX to NO, and NO increases surface acti-ity by 28% and 42%/, respectively; irradiation of these samples with one Mrad gives no additional en-

hancement.

The increased rate of thermal decomposition is not specific to radiation-enhanced surface activitypromoted by water vapors, but is found to be a function of gamma-ray interaction with bulk moleculesas well. However, the increased rates of thermal decomposition of unirradiated samples of y-IMXexposed to NO and NO, are attributed solely to thermally unstable reaction products of NO-IIMX and

NO,-HMX surface adducts.

DDPR. 1473 UNCLASSIFIED

Security Classification

UlNCLASSIFIlEDS -erurilv CI,.ssificanron Ir*LiW*IE

Tiadiometric determinat ionInteratomic distant evan der VWaals forceC;rystal structure

ThtermalI dec'ompo.sition

C:ompton int.-ractionliddiation-enhanct'd surface activityMass spectrome tryStr'aryl trimethyl ammuonium bromide

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