STUDY INTO THE INFLUENCE OF TEMPERATURE AND TIME FACTORS (160 C, 1-7 DAYS) ON HMX STRUCTURE (#254)

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1 STUDY INTO THE INFLUENCE OF TEMPERATURE AND TIME FACTORS (160 C, 1-7 DAYS) ON HMX STRUCTURE (#254) T.Ye. Kisanova, V.N. Geman, A.M. Zlobin, T.G. Kiianova, Ye.S. Kozlova, V.N. Kolesnikova, S.P. Lobanova, Yu.P. Olikov, A.M. Poduets, A.K. Fisenko, L.V. Fomicheva All-Russia Scientific Reseach Institute of Expeimental Physics (VNIIEF), , Saov, Nijni Novgood egion, Russia This pape pesents the esults of studies into tempeatue and time ects (160 C, 1-7 days) poduced on HMX. HMX cystals (C 4 H 8 O 8 N 8 ) of β fom having S sp 300cm 2 /g and S sp 300 cm 2 /g specific suface aea wee chosen as the subject of investigation to study HMX phase tansition conditions. To study HMX stuctue and its physical and chemical popeties, such techniques as optical micoscopy, themogaphy, IR spectoscopy, X-ay analysis and a pycnometic density detemination method wee used. It has been shown that HMX expeiences no polymophic tansfomation at 160 C close to the shooting appaatus opeation tempeatue and afte 1-7 days of its aging. It has been found out that heating at 160 C duing 7 days esults in decease in the density of HMX cystals fom 1.901g.cm 3 to g/cm 3. Even on the fist days of themal aging lage HMX cystals (S sp 300 cm 2 /g) have many intenal and suface defects and become tubid. All these ects ae the esult of complicated pocesses poceeding in the cystal body duing themal aging. The change in the micostuctue and density of the studied HMX cystals made it possible to assume that thee ae etained gases in the cystal body. It has been shown that etained gases may be poduced in HMX cystals. INTRODUCTION It is known that HMX is univalled among othe explosives in its pactically impotant chaacteistics such as powe, density, themal stability, etc 1,2. Specialists of VNIIEF and VNIITF contibuted geatly into studies of HMX-based explosive compositions in the 60s- 80s and they continue solving vaious technological and othe poblems now facing

2 the domestic industy. In paticula, the spead of convesion activities aimed at developing themally stable compositions fo shooting appaatus (SA) and EC opeation systems used in petoleum and gas extacting industies has been expanded 3. Fo the HE containing SA used in the oil and gas industy the poblem of study into its ultimate opeation abilities at elevated tempeatues has become ugent in ecent yeas. This is explained by a few easons, the main of which ae as follows: -oil and gas ae extacted fom inceasingly deep stata whose tempeatue is as high as 200 C and ove; -HMX being the fille of many explosive compositions used in SA expeiences polymophic tansfomations at 180 C which change geatly physical and chemical popeties of HE. Until now the infomation about phase tansfomations in the HMX samples unde study and its uppe opeation limit had a athe contadictoy chaacte although much has been done in this aea. This points to the fact that specific poblems of HMX application unde the given high tempeatue and time ects should be solved though combined studies using up-to-date physical and chemical methods such as optical and electon micoscopy, tempeatue ecoding, IRspectoscopy, X-ay analysis and a pycnometic density detemination method. Thus, study of HMX phase tansitions is a topical poblem because clea, scientifically substantiated knowledge of the limits of HMX pobable application in its vaious foms is equied. Additional checking of tempeatue and time ects poduced on the possibility of HMX polymophic tansition was the aim of this wok. The initial tempeatue of 160 C and the aging time of 1-7 days wee chosen fo studies. HMX cystals of β fom having S sp 300cm 2 /g and S sp 1500 cm 2 /g specific suface aeas wee chosen to study HMX phase tansition. Whethe HMX phase tansition was absent o pesent was detemined by the following methods: -optical micoscopy; -tempeatue ecoding; -IR-spectoscopy; -x-ay analysis; -pycnometic detemination of HMX cystal density. Duing these studies the HMX cystal habit and the changes in the main physical and chemical popeties such as cystal density, themal chaacteistics, molecula stuctue, phase composition wee monitoed. The tested HMX samples wee themally aged at the atmospheic pessue in themostats of the measuement and computation complex (MCC) Vulkan. They wee aged at 160 C±0.1 fo 1-7 days. Afte aging unde the given conditions the HMX samples wee emoved and in about half an hou (HMX cystals wee cooled to the oom tempeatue) the samples wee pepaed to be futhe tested by physical and chemical methods. STRUCTURAL STUDIES OF HMX The HMX samples (S sp 300 cm 2 /g) themally aged at 160 C±0.1 fo 1-7 days wee tested by compaison with the oiginal ones, fo which pupose light micoscopes MBS-9 wee used. Photogaphs of the cystals wee taken using MFN-5 micoscopic photogaphic attachment. In the couse of themal aging fo 1-7 days the HMX cystals (S sp 300 cm 2 /g) took on a yellowish-bown colo. The moe was the time of aging, the moe intensively changed the colo. Besides the colo change, cacking and

3 tubidity of the cystals took place. This is shown in figue 1. It has been found out that the moe is the time of heating, the less is the potion of cystals peseving thei oiginal shape and the smalle ae the fagments. It should be noted that cystal agglomeates poduced afte cacking ae typical of the tested HMX samples. Howeve, the poduced agglomeates ae not stable and they decompose afte light pessing o teating with an alcoholic-wate mixtue ( 95:5 vol.%). The HMX cystals (S sp 1500 cm 2 /g) having been themally aged at 160 C fo 1-4 days ae identical with the oiginal ones. HMX DENSITY DETERMINATION WITH A PYCNOMETRIC METHOD The densities of the tested HMX samples have been detemined with a pycnometic method which is the most popula method fo detemining densities of powde solid mateials. The eo of the tested mateial density measued with this technique is no moe ± g/cm 3. In the couse of studies it was noted that the inceased numbe of defects (such as cacks) in the themally heated S sp 300 cm 2 /g HMX caused a violent libeation of gas bubbles duing its evacuation (as opposed to the initial poduct). No phenomenon of this kind was obseved with S sp 1500 cm 2 /g HMX. The expeimental data ae given in table 1. TABLE 1. DENSITY OF HMX CRYSTALS. a c b d Type, S sp, cm 2 /g HMX chaacteistics HE density, g/cm 3 Initial HE 1.899, 1.902, av. = HE afte heating 1.835, 1.832, at 160 C, 4 days 1.834, av. = Initial HE 1.906, 1.904, HE afte heating at 160 C, 4 days av. = , 1.902, av. = e FIGURE. 1. S SP 300 CM 2 /G (A-D) AND S SP 1500 CM 2 /G (E) HMX CRYSTALS BEFORE AND AFTER HEATING AT 160 C (28 X ): A INITIAL; B 1 DAY; C 7 DAYS; D AGGLOMERATES OF SMALL CRYSTALS IN 7 DAYS; E 4 DAYS. Fom table 1 it can be seen that the density of S sp 300 cm 2 /g HMX cystals afte heating at 160 C fo 4 days deceased to g/cm 3 (the initial HMX density is g/cm 3 ). Such a geat density change must testify to fomation of new HMX phases. To suppot this suggestion, the HMX samples had to be analyzed using x-ay analysis and IRspectoscopy specifying the phase composition of the tested mateial.

4 The density of S sp 1500 cm 2 /g HMX cystals emained almost unchanged. STUDY OF THE HMX MOLECULAR STRUCTURE USING X-RAY ANALYSIS AND IR-SPECTROSCOPY X-ay analysis of the HMX having been aged at 160 C fo 1-7 days was made on the DRON-1 UM facility 1 hou afte heating using the chaacteistic coppe anode adiation. The HMX cystals being in the initial state have a stuctue that is stable unde nomal β phase conditions. Figue 2 shows x-ay photogaphs of the cystals of the initial S sp 300 cm 2 /g HMX and afte its heating. Fom the matching diffaction lines it can be seen that themal aging of the studied HMX samples esults almost in no change in its stuctue. Simila x- ay pattens wee also poduced both fo S sp 300 cm 2 /g and 1500 cm 2 /g HMX afte its aging fo 1, 3, 7 days. Thus, no phase tansfomations in the tested HMX samples having been heated at 160 C fo 1-7 days wee detected by the x-ay analysis method. S sp 300 cm 2 /g and 1500 cm 2 /g HMX having been themally aged fo 1-7 days was studied with IR-spectoscopy method using 12 mm pessed samples of HMX and potassium bomide (KB). All the samples wee tested afte 1 hou of heating. The HE specimen in the sample made up g. The HMX IR specta wee taken with IKS-24 spectophotomete ove cm -1 ange. Afte themal aging the poduced IR specta of all HMX samples ae identical to IR spectum of the initial HMX and coespond to the β- phase HMX (figue 3). Tansmition, % Wave numbes, sm -1 FIGURE 3.TYPICAL IR SPECTRUM OF β-phase HMX Rate, Pulse/s Thus, no phase changes wee evealed in the HMX samples tested by IR-spectoscopy and x-ay analysis methods afte thei heating at 160 C fo 1-7 days. The esults of X-ay analysis and IR-spectoscopy studies into the HMX samples show that the density change has esulted in no HMX phase change unde the specified heating conditions. Diffaction angle, degees FIGURE 2. X-RAY PHOTOGRAPHS OF S SP 300 CM 2 /G HMX BEFORE (1) AND AFTER 7-DAY HEATING (2) AT 160 C. STUDY OF HMX PHYSICAL AND CHEMICAL PROPERTIES

5 The HMX having been themally aged fo 1-7 days was tested by a themogaphic (diffeential-themal and themogavimetic) method using a deivatogaph of Paulis system. It has been found out that the themal chaacteistics of all tested samples ae almost no diffeent fom those of the initial HE: polymophic tansfomation of HMX occus ove C tempeatue ange, intensive decomposition is within C and the mass loss is 95%. The deivatogams of S sp 300 cm 2 /g HMX cystals befoe and afte heating ae shown in figue 4. Duing the deivatogaph tests two cucibles wee used: an open cucible 1 ( 9, h = 12 mm) and a closed cucible 2 ( 13, h = 16 mm) (Figue 5). This was done to exclude pobable ejection of the tested explosive fagments in the couse of the expeiment. Open cucible 1 Closed cucible 2 FIGURE 5. HOLDING CRUCIBLES. Duing the tests with the open cucible the themogam of S sp 300 cm 2 /g HMX afte its themal aging shows an abupt mass loss ove C tempeatue ange: afte aging fo 2 days it makes up 5%, 3 days - 3%, 4 days - 2%. The initial S sp 300 cm 2 /g HMX as well as the S sp 1500 cm 2 /g HMX befoe and afte themal aging have no abupt mass loss of this kind. No abupt mass loss was obseved ove the above tempeatue ange of polymophic tansfomation when expeimenting in the closed cucible ( 2). Afte pocessing the geneated expeimental data the authos have concluded that in case of a long themal aging unde the specified expeimental conditions a pat of gaseous themal decomposition poducts emains etained in HMX cystals o in thei fagments. Heating of HMX cystals duing themogaphic studies leads to stuctual eaangement of cystals ove the tempeatue ange of polymophic tansfomation. At the same time, the gas phase etained in the S sp 300 cm 2 /g HMX cystals gets fee. This is accompanied by an abupt mass loss (open cucible tests) testifying to ejection of HMX cystal fagments outside the cucible. а FIGURE. 4. DERIVATOGRAMS OF S SP 300 CM 2 /G HMX CRYSTALS AFTER (A) AND BEFORE (B) HEATING. b EVOLUTION OF GAS DURING HMX THERMAL DECOMPOSITION The mass m of gas in the HE volume that is govened by HE themal decomposition satisfies the following kinetic equation:

6 dm dm dm = ( ) + ( ) (1) dt dt dt dm whee ( ) is the tem descibing the gas dt elease fom the volume; dm ( ) is the tem coesponding to gas dt poduction duing HE themal decomposition. ef (dm/dt) τ = K T (m 0 -m), (2) whee m 0 is the gas mass afte HE complete decomposition (coesponds to the initial HE mass). ef K T is the ective themal decomposition constant. (dm/dt) = (m k -m)/τ, (3) whee τ 3 is the specific tempeatue dependent time of gas eleases fom the HE volume, m k is the gas mass etained in the HE volume (emaining asymptotically bound in the HE mass). Thus, dm dm mk m = ( ) +. (4) dt dt τ Duing themal decomposition the gas mass in the volume is (dm/dt) = m 0 К e t. (5) Thus, the kinetic equation takes the following fom: dm/dt = m 0 К e t -m/τ +m k /τ (6) Solution of the kinetic equation (6) may be pesented in the following fom: δ(t)= γ t/τ t/τ к t (e - e ) + δ (1 e k ),(7) γ -1 whee δ = m(t)/m 0; δ К = m k /m 0 ; γ = K. τ The gas mass poduced duing HMX themal decomposition is m т (t) = m 0 (1-e t ). (8) Accoding to (7) (8), the mass gas eleased fom the volume is m (t) = m т (t) m(t) K t 1 e γ( 1 e ) δ = δк(1 e ). (9) 1 γ Let us conside the limiting cases. 1. Slow gas elease: γ τ -1 << K = τ 1 e δк(1 e ) = (1 δк, т.е. γ K >> 1, then fom (9) we have: δ )(1 e ). (10) At τ lim δ (t) 0 as it should be. τ з = At t (t >> τ ) we get fom (10): lim δ (t) = 1 δ k. (11) This is the expected esult: fo long times the entie gas eleases except fo the etained gas. We conside the case of small times: K t << 1 при γ >> 1. In this case K t << 1 при γ >> 1. We have : t K t K t = = << 1. τз K τ γ We tansfom (9) (0) t t δ (t) δ () t δ к, (15) 2τ τ ( ) K t whee δ (0) t is the gas elease in the absence of the gas phase delay (themal decomposition).

7 This fomula allows the paametes of the poceeding eactions to be estimated duing HE themal decomposition and etention of decomposition poducts. 2. Fast gas elease: τ -1 >> K, т.е. γ << 1. Fom (9) we get: At δ (t)= 1-e τ t δ к (1 e ) t >> 1 δ (t) 1-e. (16) δ. t к At δ к << 1 themal decomposition takes place. CONCLUSIONS The studies wee caied out to test the tempeatue and time ects poduced on the possibility of polymophic tansition of S sp 300 cm 2 /g and 1500 cm 2 /g HMX aged at 160 C fo 1-7 days. They have shown that the tested HMX expeiences no phase tansfomation. Afte the studies the extenal appeaance of HMX cystals and the changes in its main physical and chemical popeties (cystal density, themal chaacteistics, molecula stuctue, phase composition) wee checked. It has been found that heating at 160 C fo 4 days leads to decease in the density of S sp 300 cm 2 /g HMX cystals fom g/cm 3 to g/cm 3. But this is not a citeion of HMX phase tansfomation. Long-tem themal aging unde the specified expeimental conditions makes a pat of gaseous themal decomposition poducts emain etained in HMX cystals o thei fagments. Futhe heating of HMX cystals duing themogaphic studies esults in stuctual eaangement of cystals ove the tempeatue ange of polymophic tansfomation. At the same time, the gas phase etained in the S sp 300 cm 2 /g HMX cystals gets fee. This is accompanied by an abupt mass loss (open cucible tests) testifying to ejection of HMX cystal fagments outside the cucible. The fomulas ae given that allow the paametes of the poceeding eactions to be estimated duing HE themal decomposition and etention of decomposition poducts. REFERENCES 1. Olova Ye.Yu. et al. HMX a themally stable explosive. M., Neda, Olova Ye.Yu. Chemisty and technology of high explosives. L., Khimiya, Vlasov Yu.A., Fomicheva L.V. On the safety limits duing explosive testing unde high-tempeatue heating conditions. Physics of combustion and explosion. 1998, v. 34, 5, pp