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US ARMYMATERIELCOMMAND TECHNICAL REPORT BRL-TR-2673

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CRITICAL ANALYSIS OF NITRAMINEDECOMPOSITION DATA: ACTIVATION

ENERGIES AND FREQUENCY FACTORSFOR HMX AND RDX DECOMPOSITION

Michael A. Schroeder DT!C.AECTE

September 1985 SEP 3 0 8

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US ARMY BALLISTIC RESEARCH LABORATORYABERDEEN PROVING GROUND, MARYLAND

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Technical Report BRL-TR-26734 TITLE (am d Subtitle) YPE OF REPRT & PERiOD CC.VERED

Critical Analysis of Nitramine Decomposition Data: FinalActivation Energies and Frequency Factors for HMXand RDX Decomposition b PERFORMING ORG. REPORT N, %1ER

7. AUTHOR(@) 6 CONTRACT OR GRANT NuMP' .

Michael A. Schroeder

9. PERFORMING ORGANIZATION NAME AND AOOREV- 10. PROG.AM ELEMENT PRO, :. TASK

US Army Ballistic Research Laboratory AREA 6 *ORK UNIT NUMBE'S

ATTN: AHXBR-IBD [ L 161 I0 2AH4 3Aberdeer Iroving Ground, MD 21005-5066

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US A,.-my Ballistic Research Laboratory n

,'.TTN: AULXBR-OD-ST .MR OF AL

Aberdeen Proving Ground, ?TD 21005-5066 12914. MONI TORINCG A.-ENCY 1N 4e 1 A -_,3LES F dIlfe.,f Iton .ontr ia 0&l. " 5 ' ''S "N -LAS! trte repnrt.

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Approved for public release; distribution unlimited.

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IS SUPPL .ME NARY NOTES

19 KE' WORDS (Continue .. rovers* mois if .-oss. a-d Ido!!v by' N'- k ;irbvrj

HMX Arrhenius Parameters DecompositionRDX Activation Energy ExplosivesNitramines Frequency Factor PropellantsKinetics Thermal Decomposition

123. ABSTRACT 1Ciritfuu. - movm,V 8*d I- o.1*C9*0" Wnf Id-nitfy, hr .. r nri.br',A literature review is presented, on kinetic parameters for thermal

decomposition of HMX and RDX in the homogeneous vapor, liquid, and dissolvedstates. The decomposition apparently fits first-order kinetics, andsuggested values for Arrhenius parameters for HMX and RDX decomposition inthe gaseous and liquid phases, and for decomposition of RDX in solution inTNT are given. The possible importance of autocatalysis is pointed outas are some possible complications that may be encountered in interpreting,

t ~Do FOR8 47 TO O ' ,O - OBS )Lf. r.. ...1 4 _ __i N _17_-0 91 O f S I s F U N C L A S S I F I ..

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S!CURITY CLASSIFICATION 14 THIS PAGEtWhr Date Znlered)

20. Abstract (Cont'd):

e xtending or extrapolating kinetic data for these compounds from measurementscarried out below their melting points to the higher temperatures andpressures characteriestic of combustion.

-,-'The mechanistic implications of the activation energies and frequencyfactors are discussed. In general, the recommended values seem cknsistentwith the idea that under many conditions the first step is either HONOelim.nation, N-NO" cleavage or some combination of these two steps. Hjwe'er,it is difficult to rule out other processes. Some possible unimolecular and

himolecular fo~lowup steps and the possible role of factors such as chainreactions, cage effects and other solvent-related effects are also discussedbriefly.

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TABLE OF CONTENTS

Page

LIST OF ILLUSTR.ATIONS.................................. .5

LIST OF TABLES .......... o......... ....... ...............

. ITemperTure Rane...... ........ so ... .... . ... . .. 0.2

C. Sublimation and Gas-Phase Reactions..*.... ................13

Do Reactions on the Container Surface.*... ........ .....15

E. Autoacceleration, Chain Reaction and Cage Effects ..... ..... 16

F. Isothermal vs Nonisothermal Thermal Analysis,*,*.,,........ .17

IV. GENERAL DISCUSSION AND SUGGESTED VALUES FOR KINETIC

C. Solution-Phase Decomposition of RDX and HMX~ooo............ 29

Do Decomposition of "Solid" 1*VC andRD............3

V.* CHEMICAL MECHANISMS ......... **.... ..... .. ....... *3

C. Unimolecular Follow-UpSep..... . .... . . .. . .38

Do Bimolecular Follow-Up Steps*.. . . . . . .. ,... .... .. .... 39

E. Extension to Combustion Conditions..............3

VI. WORK NEEDED......................... ....... 40

TABLE OF CONTENTS (Cont'd)

Page

VII. NOTES ADDED IN PROOF*.*.... .........

A.* Note Added in Proof No. 1.................4

B.* Note Added in Proof No. 2.................4

C. Note Added in Proof No. 3.................4

ACKNOWLEDEMENS... ......... . .... .......... 4

REFERENCES..4 ..... ......

APPENDIX A. REPORTED ARRHENIUS PARAMETERS FOR THERMALDECOMPOSITION OF HK AND RDX IN THE VAPOR PHASE ..............61

APPENDIX B. REPORTED ARRHENUS PARAMETERS FOR DECOMPOSITIONOF NEAT LIQUID AND DISSOLVED HMX. ....... ................... 69

APPENDIX C. REPORTED ARRHENIUS PARAMETERS FOR DECOMPOSITIONOF NEAT LIQUID AND DISSOLVED R~ .............. 7

APPENDIX D. REPORTED ARRHENIUS PARAMETERS FOR THERMALDECOMPOSITION OF HlV( AND RDX AT TEMPERATURES BELOW THEIRMELTING POINTS.o ..................... ... *toooo~ooooovo.....95

APPENDIX E. COMPUTER PROGRAM USED FOR LEAST-SQUARES FIT OFORIGINAL DATA....... o .. ... ......

APPENDIX F. COMPUTER PROGRAM USED FOR LEAST SQUARES FIT OFLOGARI~THMS OFDAA..... .....

DISTRIBUTION LIST*.......... ... .

4

LIST OF ILLUSTRATIONS

Figure Page

1. Plot of Log k vs 1000/T for Liquid RDX Decomposition ............ 21

2. Plot of Log k vs 1000/T for Decomposition of Gaseous RDX ........ 22

3. Plot of Log k vs 1000/T for Liquid HMX Decomposition ............ 23

4. Plot of Log k vs 1000/T for Gas-Phase/FMX Decomposition ......... 24

5. Plot of Log k vs 1000/T for Decomposition of RDXin Solution in TNT ......................................... 25

DTiC :

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LIST OF TABLES

Table Page

1 Suggested Log OA(sec 1) and Ea (Kcal/Mole) for ThermalDecomposition of HM'X and RDX. ... .. * ... .....

A-1 Arrhenius Parameters for Thermal Decomposition of HomogeneousGaseous HMVK AND RDX ....... ... * 65

A-2 Rate Data Used in Statistical Analysis of Gas-PhaseDecomposition of HlfX.... .................... 6

A-3 Rate Data Used in Statistical Analysis of Gas-PhaseDecomposition of RDX ............................ o.67

B-1 Arrhenius Parameters for Thermal Decomposition of NeatLiquid HMX.... ... .o . *s** . .*

B-2 Arrhenius Parameters for Thermal Decomposit~on of H1VC

R~-3 Rate Data Used in Deriving Recommended Values of ArrheniusParameters for Decomposition of Neat Liquid HMXo........77

C-1 Arrhenius Parameters for Thermal Decomposition of Homogeneous

C-2 Arrhenius Parameters for Thermal Decomposition of RDX -

Parameters foroDecompositio o..a.Lqi DX.......9

C-3 Rate Data Used in Deriving Recommended Values of Arrhenius

Parameters for Decomposition of RDX in TNT Solution ....... o..92

D-1 Arrhenius Parameters for Thermal Decomposition of RDX at andBelow its Mel.ting Point.... ... 102.....

D-2 Arrhenius Parameters for Thermal Decomposition of HNXC at and

D-3 Rate Data From Reference D-22 in Statistical Analysis ofCondensed-Phase Decomposition of RDK., .... *0 -6" 6001

D-4 Rate Data From Reference D-22 in Statistical Analysis ofCondensed Phase Decomposition of HMX... ......... ..... 110

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INTRODUCT ION

There is currently considerable interest in the use of nitramineoxidizers in gun and rocket propellantsr Tse-for example Reference 1), ue to

-their desirable properties, such as absence of noxious combustion products,high specific impulse and impetus and thermal stability. The most commonlyused nitramine oxidizers are RDX (1),talso known by such names as hexogen orcyclonite)and-currently indexed in Chemical Abstracts under the heading

"1,3,5-Triazin D hexahydro-l, 3, 5-trinitro" and'HMX (II), also known by suchnames as Octogen and indexed in Chemical Abstractsiunder the heading "1,3,5,7-.Tetrazocine, octahydro-1,3,5,7-tetranitro." K o

Before the combustion end deflagration behavior of these materials can beunderstood and intelligently modified, it will be necessary to have anunderstanding of their thermal decomposition chemistry. This is true forseveral reasons. First, combustion modellers use the kinetics and kineticparameters as input into their models. Second, the product distributions fromthe decomposition reactions are also needed as input for many of thesemodels. Also, an understanding of the detailed chemical decomposition modesmight well make it possible to suggest new types of additives for combustionmolification.

At present, the chemical mechanisms involved in the decomposition of* these materials are not at all well understood. there are a number of

apparent conflicts in the literature with regard to such topics as kineticparameters, product distributions, autocatalysis and acceleration and/orinhibition of the decomposition by substances, some cf which are knownproducts of the decomposition. Many of these apparent conflicts probablyarise from the great complexity of the decomposition. The course of thereaction seems to be very dependent on experimental conditions due to theapparent operation of simultaneous gas, liquid and solid-phase decomposition,leading to products many of which are able to react among themselves and alsoto accelerate or inhibit the decomposition of starting material. In addition,the nature of even the first step of the decomposition reaction is not at allwell understood, quite possibly as a result of variations with temperature,pressure and state of aggregation (gas, liquid, solid, dissolved in solvent)in the relative rates of the many reactions (N-N02 cleavage, HONO elimination,various forms of C-N cleavage, etc.) that have been proposed.

In view of these considerations, it appeared that there was a need for acritical, interpretative reviaw of the literature on decomposition ofnitramines, with the emphasis on HIMX and RDX. Such a review would summarize

what is known about the chemical and physical mechanisms involved, andinvolves an attempt to resolve conflicts and to suggest new experiments toelucidate the mechanisms involved.

The present report is one of a series describing such a review. Thisreview is written from the point of view of an organic chemist and so iscomplementary to reviews such as that by McCarty,' which emphasize combustion

1K. P. McCarty, "HMX Propellant Combustion Studies," AFRPL-TR-76-59 (AD-B017

527L).

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behavior as seen by a physical chemist or combustion engineer. In the presentreport, available information on kinetic parameters for HMX and RDXdecomposition is summarized, and an attempt is made to arrive at suggestedvalues for activation energies and frequency factors, and to discuss theresults in terms of the possible chemical and physical mechanisms involved inthe decomposition reartions. Brief preliminary discussions of possiblechemical mechanisms aud of needed research have already appeared,2 andsubsequent reports in the present series will deal with such topics as productdistributions and auto atalysis. There have been a number of reviews of HMXand RDX decomposition,3- 6 some of which came to our attention after thepresent work was in progress, but there still seems to be a definite need fora critical, interpretative review written from the point of view of an organicor physical-organic chemist.

In the present report, an attempt has been made to provide comprehensiveliterature coverage to approximately mid-1980, although some later reports andpapers are included.

The scope and organization of the present report are as follows: Theavailable values for activation energy and frequency factor A (expressed aslog A) are summarized in Appendices A-D. Appendix A summarizes the very fewavailable values for vapor-phase decomposition of HMX and RDX. Appendim Bsummarizes data for HMl decomposition in the neat liquid and dissolvedstates. Appendix C similarly summarizes data for RDX decomposition in theneat liquid and dissolved states. Appendix D covers decomposition of HMX andRDX at temperatures below their respective melting points. These Appendices

2(a) M. A. Schroeder, "Critical Analysis of Nitramine Decomposition Results:Some Comments on Chemical Mechanisms," Proceedings, 16th JANNAF CombustionMeeting, Naval Postgraduate School, Monterey, CA, Sep 10-14, 1979, Vol. 2,p. 17; (b) M. A. Schroeder, "Critical Analysis of Nitramine DecompositionData: Some Suggestions for Needed Research Work," Memorandum Report ARBRL-MR- 3181, Jure 1982 (AD-A116 194).

3j. Wilby, "Thermal Decomposition of RDX/TNT Mixtures, Part 1," A.R.D.E.Report (MX) 16/59, August 1959 (AD-285 991).

4 F. C. Rauch and R. B. Wainright, "Studies on Composition B," Final ReportContract No. DAAA21-68-C-0334, American Cyanamid Cominny, Feb. 1969 (AD-850928).

5M. Benreuven and L. H. Caveny, "Nitramine Monopropellant Deflagration andGeneral Nonsteady Reacting Rocket Chamber Flows," MAE Report No. 1455,Princeton University, Princeton, NJ, January 1980.

6 Ye. Yu Orlova, N. A. Orlova, et al., "Octogen-Therm3resistant Explosive,"Publishing House "Nedra," Moscow, 1975; FTD-ID (RS) T-0667-80, 2 May 1980(AD-B047 181).

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are senarately accompanied by discussions intended to justify the selection ofbest values and weights of data from each title. The 'ference numbers inthese discussions correspond to references given in thiz particularAppendix. A more general discussion of sources of error, chemical mechanism,etc. is given in the main report; this more general discussion is intended totie together the information in all of the tables, and to present suggestedvalues for kinetic parameters of hM and RDX decomposition in the liquid andgaseous states..

It should be understood that the entire decomposition process of HMXcannot be described by a single set of kinetics constants; the kinetics andparameters differ appreciably with experimental conditions such asconfinement, tewperature, pressure and phase (solid, liquid, gas, solution)and with extent of reaction. This is expcially true for the physically-complex below-the-mnelting-point decomposition, in which considerable evidenceseems consistent with the idea that initially, vaporizati3n and gas-phasedecomposition (in at least some cases probably proceeding side-by-side withtrue solid-state decomposition) leads to formation of liquid products whichcondense onto undeeomposed solid and induce liquefaction, leading toacceleration of condensed-phase decompositiot. However the rates differappreciably even between the homogeneous solid, liquid, vapor and solutionphases, and in many cases even the rate constants for homogeneous, single-phase decomposition seems subject to some autocatalysis. Thus, wnen rate datasuch as those summarized here are used for predictive purposes, care should betaken to understand as well as possible the physical and chemical mechanismsof HMX and RDX decomposition under the :onditions of pressure and temperaturefor which predictions are being made; and to take as much account as possibleof variations in physical and chemical mechanisms with temperature andpressure.

It should be remembered that the activation energies and frequencyfactors given here are the result of efforts to arrive at valuescharacteristic of certain specific chemical decomposition reactions occurrtigin the homogeneou- liquid or vapor trhases (but see the discussion in thepreceding paragraph). Consequentlyi, they are strictly applicable to complexprocesses (such as combustion) onlyi to the extent that these processes arerepresentable in terms of these same specific, homogeneous decompositionsteps. Therefore, when the values given here are used as input for c.mbustionor explosive modeling studies, they can be expected to prove most useful whenused in conjunction with other measured or estimated parameters, in modelswhich take detailed account of the individual chemical and physical processesinvolved. There is a need for further development of propellant-combustionand explosive models which take detailed account of the chemical Jecompositionprocesses involved, especially since relative rates of various initial andfollow-up steps may change with changes in pressure and temperature.

II. SOURCES OF ERROR

One important source of uncertainty in studies such as those summarizedhere is that use of a very short temperature range for the Arrhenius plot maylead to inexact values for the frequency factor and activation energies.Other important sources of error include self-heating; vaporization followedby vapor phase decomposition or by condensation onto the cooler parts of theapparatus; reactions taking place on or catalyzed by the container surface;

and autocatalysis or autoinhibition. Another problem is that it is ofter notstated whether or what sort of statistical analysis was employed. This canmake a difference, as is shown by the following example: an activation energyof 48.7 kcal/mole is regorted4 ,7 for the thermal decomposition of neat liquidRDX. In a later report in the same series, it was stated thaz least sqaaresanalysis of the data gave a log A (see- ) of 22.4 and an activation energy of

55.6 kcal/mole. This is a significant change from the earlier values I:hicwere stated to be the result of a preliminary analysis. This exampleillustrates the possible effect of statistical treatments on the results.

A. Temperature Range

Activation energy and frequency factors are determined from a logarl:'..aicplot of rate constant k vs reciprocal temperature; clearly the longer thetemperature range the more reliable will be the extrapolation t- the muchhigher temperatures characteristic of combustion and explosive behavior. Most

authors studying HMX and RDX decomposition kinetics have worked over-elatively short temperature ranges, often 20* or less, possibly because

*emperature dependence due to the relatively high (ca 50 kcal/mole) activationenergies results in shortening of the temperature range over %hich Lhedecomposition proceeds at conveniently measurable rates. This problem isespecially severe for liquid HMX, which is already within its decompositionrange at 4he melting point of solid HMX (ca 2800). In spite of this problem,Robertson was able to study neat liquid RDX over the range of 213-990 C (AT86*) and HMX over the range 271-314°C (AT - 430); the reaction .t highertemperatures was followed using a membrane manometer a"Lached to an opticallever, pressure-time traces being recorded on a moving strip of photographicpaper.

In the present report, we will plot the most reliable data on commonaxes, hoping thereby to moot the question of differences in reliability due touse of different temperature ranges in the different studic by doing commonstatistical analysis on all data for the same compound and phase.

7t

7 F. C. Rauch and A. J. Fanelli, "The Thermal Decomposition Kinetics ofHexahydro-1,3,5--rinitro-s-triazine above the Melting Point: Evidence forboth a Gas and Liquid Phase Decomposition," J. Phys. Chem., Vol. 73,p. 1604, 1969.

8 F. C. Rauch and W. P. Colman, "Studies on Composition B," Final Report,

Contract No. DAAA21-68-C-0334, American Cyanamid Company, March 1970 (AD-869-

226).

9 A. J. B. Robertson, "The Thermal Decompostrion of Explosives, Part II.Cyclotrimethylenetrinitramine and Cyclotetramethylenetetramitramine," Trans.Faraday Soc., Vol. 45, p. 85, 1949.

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B. Se I f-tieat ing

Self-heating results when an exothermic reaction generates heat fasterthan the surroundings can conduct it away. Self-heating would be favored 10 bylIrge sample sizes and by higher pressure of gas over the sample since highpressure would lead to smaller bubbles of decomposition gases, hence to less

efficient stirring of the sample. Thus two checks for self-heating would hewhether or not the rate were independent of ;a) sample size and of (b)pressure of inert gas atmosphere. Robertson found no self-heating by eithermethods for RDX with sample sizes from 4-45 mg, or for HMX with sample sizes

from 1-7 mg. Thus, it would appear that in manometric kinetic apparatus ofthis general type, use of samples of these sizes or smaller should obviate theproblem of self-heating. However, as indicated in Appendices B and C, use oflarger samples did sometimes give evidence of self-heating. Furthermore,Goshgarian in describing a DSC experiment states that "sample weight (of

H4X) greater than 1.0 mg increased the isothermal temperature during HMXdecomposition, apparently due to excess thermal evolution beyond thecapabilities of the instrument to adequately regulate a constant temperature."Thus the permissthle sample size in a DSC apparatus appears to be much smaller

* than in a standard kinetic apparatus.

If self-heating were important, it should give artificially high rateconstants at high temperatures resulting in high values for activation energyand frequency factor.

C. Sublimation and Gas-Phase Reactions

Another possible important source of error in condensed-phase studies isvaporization of the sample followed by either gas-phase decomposition, or evensublimation of undecomposed HMX or RDX onto cooler portions of the apparatus.In most of the kinetic studies, sublimation was retarded either by carryingout the reaction under a pressure of inert gas or by carrying out the reactionin an apparatus designed in such a way that all parts were evenly heated tothe temperature of the experiments. These precautions serve a purpose, sinceit is widely reported that in vacuum both 4?VX and RDX readily vaporize and

.- condense on the cooler parts of the apparltus without appreciabledecomposition; see for example Robertson.

The vapor-phase reaction can interfere appreciably with determination ofliquid-phase kinetic parameters, as shown by the results of Rogers, 12 who

* found that the vapor phase caused a quite noticeable hump on the tail of the

IOA. J. B. Robertson, "The Thermal Decomposition of Explosives, Part I.* Ethylenedinitramine and Tetryl, "Trans. Faraday Soc., Vol. 44, p. 677,0 1948.

11B. B. Goshgartan, "The Thermal Decomposition of Cyclotrimethylene-trinitramine (RDX) and Cyclotetramethylenetetranitramine (HMX)," AFRPL-TR-78-76 (AD-B032-275L).

1 2 R. N. Rogers, "The Determination of Condensed Phase Kinetics Constants,"

Thermochimica Acta, Vol. 9, p.444, 1974.

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DSC curve of decomposing RDX. The gas-.phase material disappears immediatelyaifter the liquid-phase is all gone; the result is a hump on the tail of theDSC curve at the point where liquid-phase decomposition ends and the gas-phaseRDX starts to disappear. While liquid-phase is present, what is actuallybeing observed is presumably a superposition of a first-order liquid phasereaction and a gas-phase reaction which reduces to apparent zero-order due toconstant volume and to replenishment of gaseous material by vaporization ofliquid. In the case of RDX this led12 to an apparent Ea w43.1 kcal/mole andA = 2.44 x 1016 sec - i. When the vapor-phase reaction was taken account of by'ising a baseline based on the constant gas-phase decomposition, Rogersobtained Ea = 47.1 kcal/mole and A = 2.02 x 1018 sec- 1, in good agreement with

Robertson's manometric values. In spite of Roger's publication, subsequentworkers have generally continued to ignore the vapor-phase contribution to thedecomposition of neat liquid HMX and RDX.

The above discussion refers to isothermal DSC. When temperatuce-programmed nonisothermal DSC is employed, the problem becomes even worse due

Lo probable temperature dependence of the relative importance of vai l:-andliquid-phase decomposition, as well as error introduced by the particularmethod of calculation employed.

Thus, out of the multitude of thermal analysis studies of Arrheniuspirameters of HMX/RDX decomposition, the gas-decomposition-corrected values ofRogers12' 13 are preferred. The 4 kcal/mole difference between Rogers'corrected and uncorrected activaldon energies for RDX suggests that a similarcorrection should be applied to all isothermal DSC results; examination ofAppeadix C suggests that application of such a correction would bring these

I values into the same range as those found from non-DSC kinetic studies onRDX. See also the discussion in Section II. F.

The effect of vapor-phase decomposition may be smaller for non-DSCstudies. Rauch and Wainwright (see page 29 of Reference 4), in the course oftheir reactant-disappearance kinetic sLudies of the decomposition of liquidRDX, calculated (from vapor pressure) the percent RDX initially in the gasphase for several different combinations of reactor volume and initial weightof RT)X at 2120C. These percentages varied from 0.3 to 3.6, and seemed tunrelated to the rate constant which varied in the range 2.0*0.3 x 10-3 sec -

in a manner unrelated to the amount of RDX present in the gas phase. This issurprising, since the li iid-phase rate constant at this temperature is

) calculated to be 1.25 x 1U- 3 sec-1 , using Robertson's valuesg (A = 3.16 x1018, Ea = 47.5 kcal/mole), and the gas-phase rate constant is calculated tobe about ten times faster (1.35 x 10-2 sec -1) uging Rogers' values 14 (A =

3.14 x 1013 sec-', Ea 34.1 kcal/mole) for the gas-phas; decomposition.However, this is in agreement with Robertson's statement that his manometricresults were independent of sample weight and pressure of overlying gas.Thus, it appears that vapor reaction probably does not introduce as much errorinto non.-thermal kinetic studies as into thermal analysis studies.

13 R. N. Rogers, private communication, Los Alamos Scientific Laboratory, 1979.

'4 R. N. Rogers and G. W. Daub, "Scanning Calorimetric Determination of Vapor-

Phase Kinetic Data," Anal. Chem., Vol. 45, p. 596, 1979.

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Possible reasons for this discrepancy-include the following: (a) The DSCexperiment follows Lhe decomposition by its heat release. if the gas-phasedecomposition had a greater heat release per mole than the liquid-phasedecomposition, the DSC apparatus woould sec the gas-phase reaction as being

. proportionately more important than would the conventional kinetic* experiments, thereby necessitating a large jrrection. (b) The m/V ratio

for the DSC experiments (ca 0.5mg/0.022m1 ' 23mg/ml is generally larger- than those for conventional kinetic experiments (see for example Reference 4)

(ca 40mg/26ml u 1.5mg/ml); this might promote any exothermic reaction ofgaseous products wit% each other or with unreacted RDX, since the higler m/Vratio might tend to keep gaseous decomposition products in contact withunreacted liquid (see discussion under auto-acceleration). This effect mightconceivably operate even though gaseous products are generally allowed toescape through a small hole in the top of the DSC pan. (c) The DSC apparatusmight detect heat output from reaction of gaseous decomposition products witheach other rather than just that from decomposition of RDX itself.

The possibility should be kept in mind that some of the heat evolutionfrom the gas phase reaction may be due to reaction among the products ratherthan just decomposition of RDX; however, good first order plots and reactionorders of ca 0.9 were obtained fol the gas phase reaction so it seems likelythat the observed rate constants 4 and Arrhenius parameters (Appendix A)obtained by DSC are actually those for the gas phase decomposition of RDX and

*" HMX, although it is difficult to rule out the possibility of pseudo-first-order reaction of products. Expulsion of unreacted HMX or RDX vapor through

*! the hole in the lid of the pan might also lead to artificially high rateconstants.

The above discussion applies specifically to RDX but since HX alsoexhibits a vapor phase reaction it should apply to HMX .also. However, the

,'. situation may be more complicated for HHX; see discussion in Appendix B.

". D. Reactions on the Container Surface

In connection with fs-phase decomposition, another possible (and often-* overlooked) complication is the fact that reactions assumed to take place

entirely in the homogeneous gas phase sometimes in fact take place on or arecatalyzed by the wall of the reaction vessel. More work is needed, but wallreactions are probably not a very important source or error in studies of gas-phase decomposition of H,. and RDX themselves. This tentative conclusion is

15p J Robinson and K. A. Holbrook, "Uniniolecular Reactions," Wiley-Interscience New York, pp. 6-7, 1972.

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based on two observations: First, it has been reported16 that the rate of

gas-phase HMX pyrolysis is independent of the nature of the container surface(note however, that dimathylnitramine decomposition did exhibit such adependency1 6 ); second, consider the gas-phase decomposition data for RDX

plotted in Figure 2. As stated in Appendix A and in the section on"Statistical Analysis," the data plotted includes DSC data of References A-iand A-4, and manometric data from Reference A-3. The DSC data were done inmetal-walled DSC pans. The wall material of the manometric (Reference A-3)studies was not stated, but was presumably some kind of glass or quartz. Ifthis is the case, the close correspondence (Figure 2) of data with the two

,. types of wall material would seem to suggest that wall material doesn't makemuch difference, and hence that wall reactions are not to important. Note

again, however, that the SRI workers16 found that the rate ofdimethylnitramine decomposition did depend on wall material; thus wallmaterial is apparently important at least for the case of this onenitramine. Note also the disrrepancy between dimethylnitramine and HX{ inthis respect; possible explanations include structural effects on absorptioncharacteristics, differences in decomposition mechanism, and difference in

pressure at which the experiments were carried out. See also paragraph 6 of

Note Added in Proof No. 3.

This apparent importance of wall reactions for at least some nitraminesshould be kept in mind when reading previous work on gas-phase decompositionof nitramines. Furthermore, it is recommended that future workers ondecomposition of nitramines under conditions where gas-phase decomposition maybe important, should at least check for wall reactions by examining the effect

of addel glass beads, glass wool, etc., if practicable it would probably alsobe a good idea to study the effect of variations in wall material.15 Asdiscussed above, it appears that HMX and RDX themselves may not he affectedtoo much by wall reactions, but more information is needed here also.

E. Autoacceleration, Chain Reaction and Cage Effects

In the homogenous liquid phase, autoacceleration of decomposition byproducts might be swallowed up in the overall first order rate constant if the

autoacceleratory follow-up reactions were rapid and the chain lengthsrelatively short. Robertson9 reported some evidence of autocatalysi3 of RDXdecomposition, apparently by a stable product formed in solution.Autoacceleratory behavior might in principle be expected to either raise orlower the apparent activation energy depending on the relative temperaturedependencies of the initial cleavage and autocatalyic follow-up steps, butlowering seems to be the usual pattern. Evidence for some effect on liquiddecomposition by gaseous products is provided by observations that theactivation energies for RDX decomposition were about 15 kcal/mole lower for

16D. F. McMillen, J. R. Barker, K. E. Lewis, P. L. Travor and D. M. Golden,"Mechanisms of Nitramine Decomposition: Very-Low Pressure Pyrolysis of HMX

and Dimethylnitramine," Final Report, SRI Project "YU-5787, 18 June 1979(SAN 0115/117). (Supported by Department of Energy through LawrenceLivermore Laboratories).

16

//

1

closed pan (sealed) than for open pan (1 hole) DSC experiments.17 Notehowever the possibility of heat effects due to confinement of reactive gaseousproducts. In general, however, the agreement of the most reliable rateconstants and activation energies with each other and with the vapor-phase-reaction-corrected DSC results suggests that under these conditions of less

* confinement (lower m/V ratio), rate constants are not being affected byreaction of gaseous products with the liquid phase. It is alLo possible thatcase effects could affect rates and activation parameters. See also Section VA and Note Added in Proof No. 2.

- IF. Isothermal vs. Nonisothermal Thermal Analysis

Two general aporoaches are generally used in measuring activationenergies and frequency factors by thermal analysis methods. We will refer tothese as isothermal and nonisothermal approaches. In the first (isothermal)approach the decomposing sample is held at constant temperature and the plot

R of heat evolved vs time is used to derive the rate constant at thattemperature; the rate constants derived in this way at several te-peraturesare then used in a conventional Arrhenius plot of log of k vs 1/T to derive Eaand A. In the second (nonisothermal) approach the activation energy is

• .derived by any of a variety of calculation procedures from time-propertycurves derived from programmed temperature runs.

The isothermal method seems capable of giving good results for the liquidphase reaction provided a correction is made for the gas phase reaction whichoccurs simultaneously with liquid phase reaction; thus the activation energy

* and frequency factor found for decomposing liquid RDX1 2 were 43.1 kcal/moleand 2.44 x 1016 sec - I respectively without corrections for vapor phasereaction, and 47.1 kcal/mole and 2.02 x 1018 sec-1 with correction for gasphase reaction, the latter pair of values being in reasonable agreement with

• "Robertson's values9 of 47.5 kcal/mole and 3.16 x 1018 sec- 1 (not 2.17 x 1018

sec - as stated in Reference 12). As far as this writer is aware, this is theonly attempt at correcting isothermal DSC data on liquid HMX and RDX forconcurrent vapor phase reaction; since the correction in activation energy

I seems to be about 47.1 - 43.1 - 4.0 kcal/mole and other isothermal DSC values(Appendix C, References 13, 14, 16, 20, 28-30) are generally in the range40-44 kcal/mole it would appear that applicatibn of this correction wouldraise these values to the range 44-48 kcal/mole in better agreement withRobertson's value9 of 47.5 kcal/mole. A similar treatment suggests that thecorrection factor in A is about I02 or 103; thus it is recommended that

* whenever possible values of Ea and A measured by thermoanalytical methods forliquid phase HMX and RDX should be corrected for concurrent vapor phase

* decomposition.

In the case of the nonisothermal approach it is hard to know how toinclude a correction for the gas phase reaction. In addition these methodsare generally subject to errors both experimentally and because of assumptionsintroduced in the course of deriving the equations used in the calnulation

b17

17K. Kishnre, "Thermal Decomposition Studies on Hexahydro-1,3,5-trinitro-s-triazine (RDX) by Differential Scanning Calorimetry," Propellants and

• "Explosives, Vol. 2, p. 78, 1977.

17

i / " N.. I' /

7 (see for example Reference3 18-21). Because of these considerations, and due

' ,/ to time limitations only a short discussion of non-isothermal DSC/ determinations will be given here. However, an attempt has been made at

/7 including in the Appendices all available values measured by these methods.

For example, it seems appropriate to point out that it appears1 8-20 thatone common method2 l for calculating activation energien., namely the method ofKissinger,2 1 may be subject to errors, when used to study HMK and RDXdecomposition. In particular Rogers and Smith reported20 that the Kissingermethod gave low values for activation energy (28 kcal/mole) and frequencyfactors (log A(sec- 1) - 10.6 although several olher mee:hods gave values more

in agreement with Robertson.; However, Kishorel/ 922 fotd that the Kissinger

method gave Ea = 42 kcal/mole, in approximate agreement with isothermal andother scanning methodG. Thus, it would appear that until this situation isbetter understood, the Kissinger method and other nonisothermal methods shouldbe used with caution; care stiould be taken that the system under studyconforms to the assumptions made in deriving the method. Actually, thephysical co:plexities alone may well render HMN and RDX decompositionunsuitable for study by many nonisothermal methods.

It also seems worth mentioning that several papers1 7 .20 ,2 3 include

comparisons of Arrhenius parameters, obtained by various dynamic ornonisothermal thermoanalytical methods, including DSC and TGA results. Ingeneral, the dependence of the results of these studies on experimentalconditions and method of calculation appears to be such that, as suggested byGarn2 (for systems other than HHX and RDX), it actually seems moreappropriate to regard them as "Temperature Coefficients of Reaction" ratherthan "Activation Energies," since they almost certainly do not represent anenergy of reaction for a single, homogeneous chemical process, but rather the

18W. W. Wendlandt, "Thermal Methods of Analysis," 2nd. Edition, John Wiley and

Sons, New York, NY, p. 187-193, 1974.9 . H. Sharp, "Differential Thermal Analysis," R. C. Mackenzie, ed., Vol. 2,

Chapter 28, See especially p. 55, Academic Press, New York, NY, 1972.

20R. N. Rogers and L. C. Smith, "Application of Scanning Calorimetry to the

Study of Chemical Kinetics," Thermochimica Acta, Vol. I, p. 1, 1970.

2 1H. E. Kissinger, "Reaction Kinetics in Differential Thermal Analysis," Anal.

Chem., Vol. 29, p. 1702, 1957.

2 2K. Kishore, "Comparative Studies on the Decomposition Behavior of Secondary

Explosives RDX and H1X," Defense Science Journal, Vol. 18, p. 59, See Chem.

Abstr., Vol. 90, 206758V, 1978.

2 3B. D. Smith, "Differential Thermal Analysis and Dynamic Thermogravimetric

Analysis Studies of RDX and HMX," NWL Technical Report TR-2316, July 1969(AD-857 655).

2 4p. D. Carn, "Temperature Coefficient of Reaction," Thermochimica Acta,

Vol. 28, p. 185, 1977./

7 / 18

...- .. ! /

temperature dependence of a complex process involving both vapor and condensedphase, and most likely some degree of autocatalysis as well. Thus, althoughthese methods may well have usefulness in studying trends in data for a seriesof experiments under similar conditions, the absolute values probably havemeaning only under the exact conditions for which they were determined.

Ill. STATISTICAL ANALYSIS

The statistical analysis was carried out by two methods. The firstmethod was the method of Cvetanovic and Singleton2 5 ,26 which involves fittingthe logarithms of the data using a transformation of the weights. The result

a least squares fit of the original data. The progran used had beenwritten for another project by Dr. T. P. foffee, and a copy of it is includedas Appendix E. rhe second program fits data to the logarithmic form (log kclog A - Ea/RT) of the Arrhenius Equation. The result is a least squares fitof the logarithms of the data. This program was written by D.R. Crosley and

G.E. Keller for other work. A copy of this program is included as Appendix Fof the present report. The author thanks Drs. Coffee and Keller for carryingout the analyses of the data using their respective programs.

Data on gas-phase decomposition of HMX and RDX was taken from Tables A-2and A-3 of Appendix A. These Tables include all data known to the presentwriter on gas-phase decomposition of HMX and RDX. Data analyzed fordecomposition of neat liquid HMX were taken from Table B-3 of Appendix B;these are believed by the present writer to be the most reliable data ondecomposition of neat liquid HMX. Although all three sets of data wereanalyzed and plotted together, it is suggested that until the question of thegas-phase correction for HMX decomposition is better understood, the bestvalue for liquid HM would probably be those derived from Robertson's work(Reference 9). The data analyzed for decomposition of neat liquid RDX weretaken from Table C-3; for reasons discussed in Appendix C, these are believedby the present writer to be the best data for decomposition of neat liquid

RDX. Since several authors reported data (Table C-4) on decomp-isition of RDXin TNT solution, these data were analyzed and plotted together also. The datafor neat, liquid RDX, gaseous RDX, neat liquid HMX, gaseous HMX, and RDX inTNT solution are plotted in Figures 1-5 respectively, and the Arrheniusparameters obtained from the two programs are summarized in the first fourcolumns of data in the Table. The last two columns of data in the Table listthe values suggested by the present writer for decomposition of the indicatedcompounds in the indicated state of aggregation. In general, these are thevalues from the Cvetanovic-Singleton Program, as it seems that the direct fitto the logarithmic form should be more accurate.25

,2

25 R. J. Cvetanovic and D. L. Singleton, "Comment on the Evaluation of the

Arrhenius Parameters by the Least Squares Method," Int. J. Chem. Kinet.,Vol. 9, p. 481, 1977.

2 6 R. J. Cvetanovic and D. L. Singleton, "Comment on the Evaluation of the

Arrhenius Parameters by the Least Squares Method," Int. J. Chem. Kinet.,

Vol. 9, p. 1007, 1977.

19

04 C 00

C-4 eq ~0z n ulC

0 t

be b, ND Ny d e 00 07 N0

t0i0 0 = -4 1 - - - - 00

to -

0 o N N co. 11 0 c1

- A.-U. 41cu 0; a C

+1 -4 4 H +1 4 -Im vi U C 8a 4, 0% C-4 -4? to

Wl ro a a , Nn M

> 0-

0 * *4

0. .1 z4-.

CL 44 00. 0~ r. a

ow a .44

0 L 00 m 0 41wtU U 0 v'a N . U41

-~~(A a' .

a) 04141 - 0NC

(4.-I~~ I" ( ,

4.8 o'01- a'0

0-ROBERTSON, TRANS FARADAYSOC. 5, 85 (1949)

1.01 0- RAUCH & COLMAN, 1970(AD-869-226) STUDIESON COMPOSITiON B

A-JOYNER, NWC TP 4709(AD-500-s 73)

V-R. N. ROGERS, LASL, PRIVATE0 . COMMUNICATION, 1980

SEE ALSO ROGERSTHERMOCHIM ACTA,.2,444 (1974)

-1.01o Ea=47.78 kcol/mole

-3 POINTS(V)- Log A (s-1 ) 18.E68

-2.01

2 PO INTS(j-0

-3.0

1.6 1.3 2.0 2.21000/T (*K)

Figure 1. Plot of Log k vs 1000/T ir Liquid RDX Decomposition.

21

CV)

C14

E 0-

N 0

U-

- 0

' A ' S. 0

C- <..Z C4d E<00 0

0~ 0. U

Zo%. 0 E-8

0 C3

LU- U -N~-t

0oj~ J.

oo 2 ** VZ 1 ~s 4f1601

o. ad0 C40

UO

_4U w do

0O z z

II- 00

0 00u--- um 4..E

< LDru0u~ .w ZnU-eEna. -

~. Go

0 inag -

~ g.o It2:-t in o -

Z jin< 0 im 4

00 cjwu

0 0 co*~~

0 oz0

uC'4

co

00

ui0

23

2 0 D.F. Mc MILLEN, PRIVATECOMMUNICATION OF DATAUSED IN McMILLEN, et alFINAL REPORT ON SRIPROJECT PYU 5787, FIG. 3

0 0 R.N. ROGERS, PRIVATECOMMUNICATION OF DATAUSED IN ROGERS AND DAUBANAL. CHEM, 1U, 596 FIG 7

A BELYAYEVA,etal, FTD-ID(RS)T- 1209- 78

0- E0

~E z0 E 0 35kcal /moleSLog A (s-1 ) 12.8

0

-2

-1

'24

0

0 JGYNER, NWC TP 4709(AD-500-573)

Ol WILBYARDE REPORT (MX)16/59 (AD-225-997)

-- ROBERTSON, TRANS FARADAYSOC A.585 (1949)

COLMAN & RAUCHAD-881- 190

-2go 4 :39.4 kcol/mole

Log A(s- 1) a 14.992

0

3

S Eo i 4.T 3 kcal/mlel

Log A (s"1) • 15.383 2 POINTS (0)

-4 - -3 POINTS (0)

\

-5 ,•1.8 2.0 2.2 2.4

1000/T (*K)

Figure 5. Plot of Log k vs 1000/T for Decomposition of RDX

in Solution in TNT.

25

The values of logl0 A listed in the Table are given to three significant

figures past the decimal point, although it is highly questionable whether the

accuracy of the intercepts themselves justifies more than one such figure.

The other figures are given because it is felt that modelers may find more

precision useful in interpolating within the temperature range covered by theactual measurements, or for extrapolating to temperatures not too far outside

these ranges. Note that the original rate constanta and temperatures on which

the values given arp based, are for the most part given to three or foursignificant figures by the original authors.

IV. GENERAL DISCUSSION AND SUGGESTED VALUES FOR KINETIC PARAMETERS

A. Gas-Phase

There is a need for more work on the gas-phase kinetic parameters for HM

and RDX decompositions, as mentioned in the discussion of data in Appendix A.

The best values for use in modeling studies involving gas-phase decompositionat relacively low temperatires kca 200-300

0C) would probably be log A (sec-1 )

= 11.991 and Ea = 30.5 kcal/nmle for RDX, based on the plot and statisticalanalysis of all data (Table and Figure 2). For HMX, the data is too scattered

to allow choice of a single recommended value (Table, Figure 4) but the values

are most jikely in the range 30-35 kcal/mole and log A (Sec-ly. 12.8

respectively. Until more data is available, Ea = 32.5 kcal/mole would

probably be as good :is anything.

Furthermore, there is reason to suspect that as temperature rises the

Arrhenius parameters may change appreciably, due to a change in decompositionn,chanism. This follows from the report by McMillen et al., 16 who carried out

thermochemical estimations, very low pressure pyrolysis and mas; sp..Cralstudies on gas phase HMX and dimethyl-N-nitroamine decomposition; theirresults were in agreement with the idea that at lower temperatures theprincipal reaction in the vapor phase was HONO elimination, and at higher

temperatures N-NO2 cleavage, with the cross-over point occurring at about500 0K or 300 C. If this is the case, it might be a good idea if possible torepresent the low temperature reaction by the values given above. The hightemperature N-NO2 cleavage reaction could be represented by rhe parameters22Y7estimated by Shaw and Walker for N-NO2 cleavage of HMX: log A (sec-) -

16.4 and Ea = 46.2 kcal/mole. For RDX Ea should be about the same but log Amight be expected to be lowered from 16.40 to 16.28 since RDX has only threeequivalent N-NO 2 groupings. If pessible it would probably be best for

modelers to incorporate this possible mechanism shift by representing low

temperature reactions as proceeding on the basis of whatever temperature-s-predicted by the model under consideration. Note also that the exact location

of the crossover point is uncertain; thus Shaw and Walker,27 using a somewhatdifferent set of parameters, got a crossover point of ca 60°C. In closing, we

2 7R. Shaw and F. E. Walker, "Estimated Kinetic, and Thermochemistry of Some

Initial Unimolecular Reactions in the rhermal Decomposition of 1,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane in the Gas Phase," J. Phys. Chem.Vol. 81, p. 2572, 1977.

26

point out again that there is a need for more data on the gas-phase*.- decomposition of both HM and RDX, especially in the high-temperature range,*where N-N02 cleavage may become important.

Available data on gas-phase decomposition of nitramines other than HKKand RDX has been summarized by the SRI group, 16 who also carried outadditional measurements themselves, on dimethylnitramine and HMX. The

"" literature 2 8 3 1 activation energies and frequency factors varied widely (Eavalues reported for dimethylnitramine varied from 37 to 53 kcal/mole, forexample), and were generally interpreted as being consistent with log A(sec - I)

12.4 and Ea = 35-39 kcal/mole, or with log A(sec- ) = 16.5 and Ea = 43-48kcal/mole. These values were of interest because they are characteristic ofHONO elimination, and of N-NO2 cleavage respectively. The SRI workersinterpreted their results in terms of temperature-variation of the relativeimportance of these two mechanisms, see the preceding paragraph. However, tnierole of wall reactions seems uncertain at this point. As pointed out by the

* SRI workers, 16 the apparent lack of surface effects on HM decomposition seems* puzzling, since dimethylnitramine decomposed faster with a normally aged or- oxygen cleaned surface than with a carbon-coated surface. On the other hand,

the decomposition rate of N-methyl-N-choloromethylnitramine was unaffected byincreasing the specific surface area of the container by over an order of

* magnitude,3 1 and Figure I of Reference 30 suggests that decomposition kineticsof 4tethylnitramine were not greatly affectea by filling the reaction vesselw..n glass packing. The explanation for these results seems uncertain;

S :i differences in pressure between experiments may make a difference, orpossibily the surface reaction has a steric requirement that is satisfied onlyby the relatively unhindered dimethylnitramine. In any case, there is clearlya need for further work on the nature and occurrence of surface reactions inthe gas phase decomposition of gaseous nitramines, if the gas-phase

• decomposition itself is to be understood.

* B. Liquid phase

The activation energy and frequency factors from the four apparently mostreliable data sources on decomposition of liquid RDX have been described inAppendix C and accompanying discussion. A plot of the data for all four

"" sources on one axis is given in Figure 1, and a statistical analysis of the

2 8 j. M. Fluornoy, "Thermal Decomposition of Gaseous Dimethylnitramine," J.

Chem. Phys., Vol. 36, p. 1106, 1962.

B. L. Korsunskii, and F. I. Dubovitskii, "Thermal Decomposition Kinetics of

N, N-Dimethylnitroamine," Dokl. Akad. Nauk. SSSR, Vol. 155, p. 402, (Eng.Trans. p.266), 1964.

"." 30 B. L. Korsunskii, F. I. Dubovitskii, and E. A. Shurygin, "Kinetics of theThermal Decomposition of N-N-Diethylnitroamine and N-Nitropiperidine,"Izvest. Akad. Nauk. SSSR, Ser. Khim., p. 1452, (Eng. Transl. p. 1405), 1967.

3 1B. L. Korsunskii, F. I. Dubovitskii and V. I. Losenova, "ThermalDecomposition Kinetics of N-Methyl-N-Chloromethylnitramine," Russian J.Phys. Chem., Vol. 43, p. 645, 1969.

27

//

points for all four sources by he procedure of Cvetanov[c and Singleton

(pp. 19-26) gave A = 2.46 x 101 (log A = 18.668) and Ea = 47.8 kcal/mole:these are our suggested values for decomposition of neat liquid RDN.

Tho values for neat liq,,id HIX were similarily discussed in thediscussion accompanying Appendix B. The most reliable values9,13,32 are thosethat were plotted (Figure 3), and analyzed siilarily to the PDX values givingvalues for log A and F which could possibly he presented as recommendedvalues for modeling studies Involving decomposition of pure liquid HIMY. Note,however, Ja 4while the picture of concurrent gas and liquid phasereactions . still seems to hold for RDY. it has ctly begun to appearthat the situation for HMX may be more complicated,'' J and until thissituation is understood better 6han at present, it may be a good idea to just

use Robertson's manometric data as the best data for decomposition of neatliquid HMX: as shown in Appendix B. this gives Fa = 53.1 kcTl/mole and log A

(sec - ) = 19.950. Note also that the values of log A (sec- ) (= 21-21.5)obtained from all three sets of data together seem unreasonably high.Alternatively, Robertson's values of E 52.7 kcal/mole and log A (sec-) =a19.7 could be used, especially since some of the discrepancy between the two

sets was presumably introduced by the present writer in the course of readingnumbers off Robertson's' published graph.

I

I

3 2R. J. Powers, AFATL, Eglin AFB, FL, Private Communication, 1980.

3R.N. Rogers, Los Alamor, Scientific Laboratories, Private Communication,1980.

28

.K

Activation energies for thermal decomposition of nitramines other thanHM and RDX 0 ,3 4 -3 9 in the neat liquid state are generally in the range 40W5kcal/mole, with frequency factors correspondingly decreased. The values hagbeen observed to decrease with increasing confinement in at least one case,--

namely that of di-(2-nitroxyethyl)-N-nitroamine; this was attributed35 toautoacceleration due to a combination of hydrolysis ard oxidation involvingwater and NO2 formed in the decomposition.

C. Solution-Phase Decomposition of RDX and HMX

Activation energies and log A for solution phase decomposition of HMW. andRDX are summarized in Appendix B (HMX) and Appendix C (RDX). Like the gas-phase values the values for frequency factors and activation energy aregenerally lower for decomposition in solution than in pure liquid. There wasenough data on the decomposition of RDX in solution in TNT to allowstatistical analysis by the procedure of Cvetanovic and Singleton; a plot isgiven in Figure 5. The line for the three studies at concentration of 20-60%falls above the line defined by the studies of Robertson (carried out atconcentrations of 1-5% RDX) within the region studied experimentally, althoughthe frequency factor for the 20-60% points is lower than that for the 1-5%points; apparently there is a line crossing resulting from a slightly higheractivation energy for the 1-5% studies. It is not certain whether tMis line

S crossing is real or is an artifact resulting from scatter in the experimentaldata. If, as it does not seem altogether unreasonable, the line-crossing is aartifact, then it would appear that the studies at 20-60% concentration have afrequency factor higher by a factor of ca 2-3 than the studies at 1-5% RDX.

34 F. I. Dubovitskii, C. B. Manelis and L. P. Smirnov, "Kinetics of the ThermalDecomposition of N-Methyl-N, 2, 4, 6-Tetrnitroaniline (Tetryl)," RussianJournal of Physical Chemistry, Vol. 35, p. 255, 1961.

35F. I. Dubovitskii, Yu. I. Rubtsov, V. V. Barykin and G. B. Manelis,"Kinetics of Thermal Decomposition of Diethylnitramine Dinitrate," Bull.Acad. Sci. USSR, Div. Chem. Scd•, p. 1126, 1960.

36B. S. Svetlov and B. A. Lur'e, "Thermal Decomposition of Di(nitroxyethyl)

nitramine," Russian Journal of Physical Chemistry, Vol. 37, p. 1073, 1963.

* 37N. G. Samoilenko, A. A. Vinokurov, V. G. Abramov and A. G. Merzhanov,"Kinetics of the Thermal Decomposition of Dinitroxydiethylnitramine with noRemoval of Gas from the Reaction Zone," Russian Journal of PhysicalChemistry, Vol. 44, p. 22.

38B. L. Korsunskii, L. Ya. Kiseleva, V. I. Ramushev and F. I. Dubovitskii,* "Kinetics of the Thermal Decomposition of bis-(2,2-Dinitropropyl)-N-

nitroamine," Izv. Akad. Nauk. SSSR, Ser. Khim., p. 1778, (Eng. Transl.,p. 1699) 1974.

3 9G. V. Sitonin, B. L. Korsunskii, N. F. Pyamakov, Y. G. Shvaiko, I. Sh.Abrakhmov and F. I. Dubovitskii, "The Kinetics of the Thermal Decompositionof N,N-Dinitropiperazine and 1,3-Dinitro-1,3-Diazacyclopentane," Izv. Akad.Nauk. SSSR, Ser. Khim., p. 311, (Engl. Transl., p. 284) 1979.

29

However, the possibility of a systematic error in the I-5% studies should bekent in mind, since these studies are all taken from a single publication.Continuing this possible trend, the frequency factor for decomposition of neat

"- liguid RDX is considerably higher than for the reactions in solution (2.46 x* 10 8 sec', Figure 1). The values for gas-phase decomposition (Table, p. 26-

27) are also lower than tor the neat liquid; possible reasons for thisincrease in frequency fpztor with concentration include (a) a difference inmechanism of energy transfer leading to an increase with RDX concentration inthe efficiency of energy transfer into RDX molecules; (b) an increase with RDX

=. concentration in the importance of bimolecular follow-up steps much as thosediscussed in our discussions2a' of possible mechanisms involved in HM%^and RDXdecomposition; and (c) catalysis of TNT decomposition by solute RDX.

For both HMX and RDX, the activation energies for decomposition insolution (Appendices B, C and Figure 5) are generally lower (ca 40-45kcal/mole) than those (ca 50 kcal/mole) for decomposition in the neat liquidphase (Appendices B, C and Figures 1 and 3). The best values for the vapor-phase decomposition of both compounds are also lower than for the neatliquid. Possible reasons for this include the following: (a) the mechanismchanges from one unimolecular mechanism to another on going from gas phase orsolution to neat liquid HMX; (b) the mechanism stays the same, but neat liquidHMX and RDX exerts a different solvent effect than the itiert solvents studied;(c) the mechanism shifts from unimolecular in the gas.-phase or in dilute

* solutions, to bimolecular, possibly chain or autocatalytic, in neat liquid HMXor RDX. Possible bimolecular steps might include reaction of a nitro group onone molecule of HMX or RDX with a CH2 grouping of another HMX or RDX molecule,

*" as illustrated in Scheme VI of Reference 2-A, or electron transfer between two• " molecules of HMX or RDX. A bimolecular first step for the decomposition in

the neat liquid is not inconsistent with the observed first-order kinetics,since the concentration of HMX/RDX seen by any given molecule of HMX/RDX wouldremain constant throughout the reaction; hence the reaction would be zero-order in the second molecule of HMX/RDX and first-order overall. However, (c)seems unlikely in view of the high (log A - 1018 - 1020) frequency factors forthe liquid-phase reaction, and of the apparent first-order kinetics insolution. See also the discussion of cage effects in Note Added in Proof No.

* 2.

In connection with the discussion of the decomposition of RDX in TNTsolution, it seems worth mentioning that while RDX catalyzed the thermal

/ . decomposition of TNT 4 0 the TNT acts as an inert solvent with regard to the

/ decomposing RDX.9 '4 0

40W. p. Colman and F. C. Rauch, "Studies on Composition B," Final Report,

Contract No. DAAA21-70-0531, American Cyanamid Company, February 1971 (AD-

881 190).

30

S I

The above values for log A and Ea are approximately in agreement withthose measured for a series of substituted dialkylnttroaminei indibutylphthalate solutions; these measurements gave log A(sec - ) 13.7-14.4and Ea - 40-42 kcal/mole. However studies on a series of 4-substituted-2,6-dinitrophenylmethyl-N-nit oamines in dinitrobenzene solution gave somewhatlower values: log A(sec - ) 12•4-13.5 and = 32-36 kcal/mole.

. .D. Decomposition of "Solid" H and RDX

The reason for putting quotation marks around the work "solid" is that inmost low temperature (100-300*C) work the decomposition of PDX and (possiblywith somewhat less certainty) HMX below their melting point may well inTolve

V the liquid and vapor phases in addition to, if not i td of, true solid-r: state decomposition. For example, Cosgrove and Owen fsund that the rate*-of decomposition of RDX at 195*C (ca 5-10 ° below its melting point) was (a)

directly proportional to the volume of the reaction vessel; (b) for a constantvolume independent of the amount of RDX present: and (c) retarded by thepressure of inert gases, for example, nitrogen. They concluded that RDX doesnot decompose in the solid state to any significant degree at thattemperature. Rather, in the early stages of the decomposition, the RDX wasconsidered to vaporize and the vapor to decompose to liquid products whichdissolve the solid and thus accelerate the decomposition.

In agreement with this, studies4 5 on decomposition of RDX at high (up to5 kbar) pressures indicate that decomposition of RDX is much slower in thesolid state just below its melting point, than in the liquid state at itsmelting point.

Since HMX and RDX are very similar chemically, these results raise strongsuspicions that H14X may behave in a similar manner when decomposed below its

-4 1R. S. Stepanov, V. N. Shan'ko, 1. P. Medvetskaya, and V. H. Gorodetskaya,

"Kinetics and Mechanism of Thermal Degradation of Certain Alkyl-andArylakylnitroamines," 5th All-Union Symposium on Combustion and Detonation,p. 56-9. (FTD-JD(RS)T-1208-78) (AD-B033 622), Sept. 1977.

42J. D. Cosgrove and A. J. Owen, "The Thermal Decomposition of 1,3,5-

Trinitrohexahydro-1.3,5-triazine (RDX)," Chem. Commun.. Vol. 286, 1968.

/ -.. 4 3J. D. Cosgrove and A. J. Owen, "The Thermal Decomposition of 1,3,5-Trinitrohexahydro-1,3,5-triazine (RDX) Part I: The Products and PhysicalParameters," Combust. Flame, Vol. 22, p. 13, 1974.

44J. D. Cosgrove and A. J. Owen, "The Thermal Decomposition of 1,3,5-Trinitrohexahydro-1,3,5-triazinc (RDX) Part II: The Effects of theProducts," Combust. Flame, Vol. 22, p. 19, 1974.

45P J. Miller, G. W. Nauflett, D. W. Carlson and J. W. Brasch, "The ThermalDecomposition of 1,3,5-trinitrohexadydro-1,3,5-triazine (RDX) and RDXd stFiah Pressures," Proceedings of the 17th JANNAF Combustion Meeting, Vol. XIp. 479, Hampton, VA, 22-26 Sept. 1980.

31

.1

melting point. In fact, Maksimov46 found that HMX did behave similarly to RDXwhen it was ,'ecomposed below its melting point, although in the case of HMX,

S•the volume diendence was not as great as for RDX. Thus the true solid-statedecomposition may well be more important for HNX than for RDX, possiblybecause HMX is solid at temperatures higher than the melting point of RDX, orbecause of lower vapor pressure for HHX than for RDX at the temperatures of

. the-respective experiments.

However, there is another point of view in the question of vapor-phaseinvolvement in "solid" HMX/RDX decomposition: Batten4750 has also studiedthe decomposition of RDX below the melting point and has interpreted hisresults in terms of positive or negative catalysis of the condensed phase

. decomposition by gaseous decomposition products.

After the publication of Batten's work, Cosgrove and Owen43 argued again- in favor of the gas-phase decomposition, saying that the results quoted by

Batten are not at variance with the suggestion 2 ,4 3 that the gas-phasedecomposition is important in the early stages of the reaction. In additionto the arguments of Cosgrove and Owen, this writer feels that it is worthnoting that Batten47 reported that with 0.4 g of RDX in a standard sampletube, the induction rate (in percent per minute) was one-half that with only0.2 g RDX in the sample tube. Since the sample size was twice as great, thiscorresponds to a constant rate of decomposition in grams/minute. Since thesame constant-volume reactor was presumably used for both experiments, this

•* result seems more consistent with vaporization and gas-phase decomposition ifit is considered that the second 0.2 g of RDX must lie underneath the first

* 0.2 g, and hence its vaporization is suppressed. In general, it seems to thiswriter that the increase in rate with increasing reactor volume, or amount ofa free space, spreading, etc., and its independence on sample weight at constant

• volume, suggest that the gas phase decomposition is important in the early. stages of the decomposition below the melting point. Note however that the

I.46

Yu 4 6 yu Ya. Maksimov, Tr. Mosk. Khim-Tekhnol, Inst. No. 53, p.73, 1967; see

* Chem. Abstr., Vol. 68, p. 41742r. Translated by H. J. Dahlby, Los Alamos,. Report LA-TR-68-Y), Los Alamos, NM, 1968.

4 7J. J. Batten and D. C. Murdie, "The Thermal Decomposition of RDX at* Temperatures Below th.e Melting Point. I. Comments on the Mechanism," Aust.

J..Chem., Vol. 23, p. 737, 1970.

J. J. Batten and 0. C. Murdie, "The Thermal Decomposition of RDX at

Temperatures Below the Melting Point. II. Activation Energy," Aust. J.Chem., Vol. 23, p. 749, 1970.

J. J. Batten, "The Thermal Decomposition of RDX at Temperatures Below theMelting Point II. Towards the Elucidation of the Mechanism," Aust. J.Chem., Vol. 24, p. 945, 1971.

-50J. J. Batten, "The Thermal Decomposition of RDX at Temperatures Below the

*Melting Point. IV. Catalysis of the Decomposition by Formaldehyde," Aust.J. Chem., Vol. 24, p. 2025, 1971.

32

"I

/

I // .. /

I . ./

decomposition residue is apparently a positive catalyst9 '4 9 ,5 1 and that suchapparent products as formaldehyde, NO2 and hydroxymethylformamide can catalyzethe reaction either positively or negatively depending on the exact reactionconditions (see for example References 44 and 49). Thus, it may well bepossible to explain just about qny set of results by some combination ofinhibition and catalysis of the condensed phase reaction by gaseous productssuch as formaldehyde and N02, expecially when the possibility of reactionbetween the-se products is considered.

Clearly, there is a need for more work on the relative roles of vapor-phase, liquid-phase, and true solid-state reaction in the decomposition of HMXand RDX below their melting points, in order that the contribution due to truesolid-state decomposition can be extracted and, extrapolated intelligently tocombustion and explosion conditions. One possible type of experiment thatmight help here would be to use various amounts of sample in varying amountsof sample tubes of similiar construction, in reactors of differing volumes butotherwise similar construction. This would make it possible to get a betteridea of the effect of sample size, configuration, and reactor volume, eachwith the others held constant. This should be done for HMX as well as forRDX.

Thus, these below-melting point activation parameters are actuallyoverall numbers for complex processes, and it is difficult to relate them toany single, homogeneous chemical reaction. Garn2 4 has suggested the use ofthe term "Temperature Coefficient of Reaction" rather than "Activation Energy"in situations of this type; the present writer agrees with this suggestion.

Furthermore, Arrhenius parameters for decomposition below the meltingpoint seem to be dependent on such factors as degree of spreading of thesample, which are difficult to evaluate in view of the limited infomationgiven in many of the reports. For example, Batten and Murdie 8 found thatactivation energies for decomposition of RDX below its melting point weredependent on the degree of spreading of the sample.

For these reasons and because of time limitations, a complete discussionand evaluation of Arrhenius parameters for decomposition of nominally "solid"HMX and RDX below the melting point does not, at this time, seem jusiified interms of its relevance to any true solid-state decomposition of propellantsthat may occur under combustion conditions. Consequently, although for futurereference an attempt has been made at including all available activationenergies for decomposition of HMX and RDX below their melting points in

Appendix D, they will not be discussed in detail; only a few trends andparticularly relevant points will be considered.

It seems worthwhile to begin the discussion of these points by sayingsomething about the relative rates of the gas, liquid and solid decompositionand their relations to combustion modeling efforts. The above-mentioned work

5 1B. Survanarayana and R. J. Graybush, "Thermal Decompositior. of 1,3,5,7-tetranitro-1,3,5-Tetrazacyclooctane (HMX); A Mass Spectrometric Study of theProducts from 8-HMX," Ind. Chim. Belg., Vol. 32, Spec. No. Part 3, p. 647,1967.

33

J 7

of Cosgrove and Owen4 2-44 indicates that the gas-phase reaction is much fasterthan the solid-state decomposition. Furthermore, the liquid-phasedecomposition is faster than the solid-phase reactlon,3 ,[ 1,14,52 even up topressures of 5 kbar.4 5 A liquid/solid rate ratio of 10/1 or greater seemsreasonable for RDX at its melting point, based on examination of the pressure-time data in Figure 8 of Reference 3. Also, decomposition of HMX acceleratessharply when it is heated past its melting point. In view of these results,it seems quite reasonable for combustion modelers to assume that the solid-

. phase decomposes relatively slowly, and that primary decomposition takesplace, almost entirely in the liquid layer or in the vapor phase. However

some, albeit slow, solid state reaction apparently does take place,5 3 even forRDX and pressures and temperatures of combustion are much higher than those atwhich the decomposition studies are carried out; it is quite possible thatthese higher temperatures and pressures may lead to accelerated solid statedecomposition. This point seems especially relevant to conditions where thereis no liquid layer. It would also help to know whether at the heating ratesinvolved in combustion, HMX has time to transform from the $- to the6-polymorph.

Another interesting trend is that, in many cases (Appendix D) HMX7 exhibits a change in activation energy in the region 240-2600 C. Sometines

there are two changes separated by ca 10-20. This break appears in theresults of studies by thermal analysis and or manometric studies, so it is nota peculiarity of any one experimental method. One possible explanation for

this might be as follows: Goshgarian (p. 13 of Reference 11) has observed anendotherm in DSC curves of HMX samples, as well as increased gas evolutinn, atca 250C. He tentatively attributes this to melting of a-HMX left over froathe 3-6 phase transition at ca 1900C, apparently following an earlier reportby Tettsov and McCrone54 that some 0-HMX survives the 8-6 phase transition an&melts at 240*C; these observations are described more fully in Reference 54 ofthe present report than in Reference 6 of Reference 11. Photographs of thiseffect are shown on pages 19-21 of Reference 1. If the 8-HMX melts, itpresumably exhibits a tendency to solidify into 6-HMX, seeded by the 6-HMXalready present. While liquid HMX was present it might decompose at a faster(preceding paragraph) rate than he solid HMX and changes with temperature inthe amount of liquid HMX present might cause a shift in temperature-dependenceof the decomposition rate, as observed. Even if the 0-HMX melt hypothesisproves incorrect, the activation energy shift might still be related to theendotherm and increase in gas evolution at 250 0 C.

5 2T. B. Joyner, "Thermal Decomposition of Explosives. Part I. Effect of

Asphalt on the Decomposition of Asphalt-Bearing Explosives," NWC TP 4709,March 1969 (AD-500 573).

5 3 J. N. Bradley, A. K. Butler, W. D. Capey, and J. R. Gilbert, "Mass

Spectrometric Study of the Thermal Decomposition cf 1,3,5-Trinitohexahydro-

1,3,5-triazine (RDX)," J. Chem. Soc., Faraday Trans. Pt. 1, Vol. 73,p. 1789, 1977.

5 4A. S. Teetsov and W. C. McCrone, Jr., "The Microscopical Study of PolymorphStability Diagrams," Miscroc Cryst-Front, Vol. 15, p. 13, 1965.

34

./* * / / .

Another interesting aspect is that DSC and Flow Reactor MassSpectrometric (FRMS) studies on pure HNX and RDX decomposing at or very close

to their melting points (Appendix D) often show very high 5 gc vation energiesof 100-201 kcal/mqle or more. These have been attributed * to thermal

chain reactions, or to the complexity of the decomposition reaction 5 or tothe ocurrence of plycesses involving the sivultaneous breaking of more than

one chemical bond, although this last seems more likely to lower than toraise the activation energy. In view of the faster decomposition rate for theliquid than for the solid state, the following explanation might also be worthconsidering: over the melting range of HMX (or RDX) a small increase in

temperature will cause some of the sulid to melt. Because of the greater

decomposition rate of the liquid, this causes the rate to increase, resultingin an artificially large temperature-dependence of the decomposition rate,until the solid is entirely melted and the temperature dependence of the

decomposition becc,acs that of the neat liquid.

V. CHEMICAL MECHANISMS

A. Autocatalysis

When decomposition takes pl'ce under very confined conditions, activation

energies for liquid decomposition of HMX and RDX can apparently be lowered dueto autocata lysis by gas-phase products. For example, when RDX wasdecomposed' in an open (one hole in lid) DSC pan F was ca 41 kcal/mole butwhen the decomposition took place in a closed pan: the rate was faster and

activation energy was ca 10-15 kcal/mole lower. A similar pattern has alsobeen observed for dinitroxydiethylnitramine; it was attributed by the authorsto a combination of hydrolysis and oxidation by NO2 formed in thedecomposition. A similar effect may hold a high pressure, where productswould have a more difficult time escaping from the surface. Thus, serious

consideration should be given to the possibility that apparent activationenergy (or temperature coefficient of reaction) might be lower under the

higher pressure characteristic of combustion conditions than the values givenabove. However, it is difficult to rule out the possibility that the above

effects might be heat effects due to confinement of reactive products near thestarting material. Also, under the higher temperatures of combustion

conditions, higher activation-energy unimolecular reactionsmight predominate.

55R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energies with

a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p. 412, 1966.

56P. G. Hall, "Thermal Decomposition and Phase Transitions in Solid

Nitramines," J. Chem. Soc., Faraday Trans. Pt. 2, Vol. 67, p. 556, 1971.

57B. V. Novazhilov, "The Temperature Dependence of the Kinetic Characteristicsof Exothermic Reactions in the Condensed Phase," Dokl. Akad. Nauk. SSSR,Vol. 154, p. 106, 1964.

4/

Dimethylnitramine decomposition also appeared subject to autocatalysis byN02.29,58 Thus, other nitramines also seem to show autocatalysis.

Furthermore, HMX and RDX decompositions have been reported to be acceleratedor retarded by addition ftnn decomposition products such as formaldehyde.and oxides of nitrogen.

There are also a number of reports (see for example References 9, 11, 49,51) of residues or stable products that are capable of accelerating thedecomposition or of lowering the decomposition temperature.

/ More work is needed in the area of autocatalysis of nitramine. HX andRDX decomposition. Since may of the references cited in the proceedingparagraph do not specifically allude to the possitglity of surface catalysis

of gas-phase reactions, and since the SRI workers found that at least some

of the rates were affected by the nature of the container surface, it would behelpful to have a better understanding of the role of surface reactions here.

B. Initial Step

As discussed previously,2 these are complex systems. However, at

preb.nt, the available data seems consistent with the idea that the mostlikely mechanism for the initial decomposition in the gaseous phase is a

combination of HONO elimination at lower temperatures and N-NO2 cleavaq2 athigher temperatures, with the crossover point occarring at about 300 0C10 or

600°K.2 7 This is based on thermochemical estimates of temperature-variation

of relative rates for the possible decomposition steps,16 on comparison of the

preliminary best values (Table) for activation energies and frequency factorswith values estimated27 for the individual processes, and on the results ofvery low -.essure pyrolysis studies 16 on dimethylnitramine decomposition.

For decomposition in the pure liquid phase, the above values for theactivation energies for decomposition of RDX (47.8 kcal/T le) and HX (53-57kcal/mole) seem reasonably close to the values estimatedz' for gas-phase N-NO2cleavage (46.2 kcal/mole), although 2he value for HMX does seem uncomfortablyclose to the 60 kcal/mole estimated2 for gas-phase unassisted C-N cleavageand is also associated with a log A (sec- 1 ) value of 1020 - 1021. which seemsunexpectedly high. However, without more detailed knowledge of the molecularand electronic structure of the transition state, it is difficult to evaluatethe effect of such factors as (a) the electrostatic effect of the other N-NO2groupings in the starting W47 or PDX, or (b) "solvent" as opposed to the gas-phase) effects of neat liquid HMX and RDX on the observed activation energies.

The activation energies for decomposition of INX and RDX in solution are

difficult to interpret. They tend to be around 40 kcal/mole, which is severalkcal/mole lower than those of the neat liquids, although not quite as low as

the vapor-phase values (ca 30-35 kcal/mole). The reasons for this areuncertain, in view of the difficulty in evaluating the solvent effects on

58 B. L. Korsunskii, F. I. Dubovitskii and G. V. Sitonina, "Kinetics of theThermal Decomposition of N,N-Dimethylnitroamine in the Presence ofFormaldehyde," Dokl. Akad. Nauk. SSSR, Vol. 174, P. 1126, 1967(Engl.Transl., p. 436).

36

/

these activation energies. One possible explanation might be that in the gas-phase and in solvents studied to date the first step is HONO elimination,while in the neat liquid it is N-NO2 cleavage, although without moreinformation it is difficult to suggest why the "solvent effect" exerted byneat liquid HMX or RDX should be so different from the other solvents. Note,however, that the studies have apparently been carried out in a temperaturerange where the intrinsic (gas phase) reactivities toward HONO elimination andN-N02 cleavage are near the crossover point; thus small variations in solventeffects could conceivably have more dramatic effects on the nature of theprincipal pathway.

possibly the main conclusion to be drawn from the activation energies isthat 'the observed values for HMX and RDX decomposition in the gaseous andliquid phases seem to be in a region (ca 30-50 kcal/mole) that is morecharacteristic of HONO elimination and N-NO2 cleavage than of the highervalues estimated2 7 for C-N cleavage, although it is difficult to rule out allpossible variations on the general theme of C-N cleavage, such as C-N cleavageinvolving two or more bonds simultaneously, expecially since unexpectedly lowactivation energies for depolymerization of trioxane to formaldehyde (areasonable model for depolymerization of RDX to N-nitroforminine) ha.! beeninterpreted in terms of a concerted ring cleavage. 59 ,60 However, some degreeof N-N cleavage must be capable of taking place, since isotope-labelingstudies on mixtures of un- and fully N-15 labelled HMX32 show some s..amblingof the labelled and unlabelled nitrogens. The scrambling most likely takesplace during the primary decomposition step, since HMX labelled in the nitrogroup with N-15 decomposes to give unscrambled N20 with the labelled nitrogenstill attached to the oxygen.A3,61 The most straightforward explanation forthe scrambling32 is ai preliminary equilibrium involving dissociation andrecombination of the N-NO2 bond.

However, it should be remembered that the activation energy for thedecomposition of neat! liquid HMX and RDX may be influenced by factors otherthan the occurrence of a single, homogeneous process. For example, it has

59S. W. Benson and H. E. O'Neal, "Kinetic Data on Gas-Phase UnimolecularReactions," NSRDS-NBS 21, p. 314ff. For sale by the Superinteudent ofDocuments, US Printing Office, Washington, DC 20402, February 1970.

60S. W. Benson, "Thermochemical Kinetics," Wiley Interscience, New York,

p. 117, 1976.

6 1B. Suryanarayana, R. J. Graybush and J. R. Autera, "Thermal Degradation of

Secondary Nitramines: A Nitrogen-15 Tracer Study of HMX (1,3,5,7-Tetranitro-l,3,5,7-Tetrazacyclooctane)", Chem. Ind., London, p. 2177, 1967.

37

. ,' .... /".\

V"

i7

(

/

been suggested6 2 ,6 3 that the higher values observed for decomposition ofnitrate esters in the liquid than in the vapor phase may be due to a decreasewith increasing temperature, in the inhibition of the reaction due torecombination of NO2 and alkoxy radical fornd in the primary 0-NO2 bond

breaking step. This decrease was suggested to be due to increasedmobility and to increased tendency for the NO2 to undergo further reaction

rather than recombination, as temperature increases. Like the nitrate esters,the nitramines exhibit higher activation energies for decomposition in theliquid than in the vapor phase, although in the case of the nitramines, thegas-phase activation energies and frequency factors seem more characteristicof HONO elimination than of N-N02 cleavage. However the above "cage" effectcould conceivably be raising the neat-liquid activation energies for Hng andRDX decomposition. In this connection it seems worth mentioning thatnitroalkanes appear to undergo BONO elimination rather than C-Niro cleavagein the gas phase, at least up to temperatures of about 450C.

64'

The frequency factors are somewhat more difficult to interpret,especially the condensed phase values. The frequency factors for the neat-liquid decompositions (Table) RDX, log A (sec-?) - 18.7; HMX log A(sec - ) -

19-22 seem unexpectedly high for a first order reaction. Although this isconsistent with the o currence of bimolecular follow-up reactions of the type

discussed previously,S it should be remembered that little if anything isknown about energy transfer processes in liquid HMX and RDX. These high

frequency factors seem inconsistent with bimolecular initial steps, or withanchimerically assisted C-N cleavage, since such mechanisms would be expectedto lead to low frequency factors due to the high degree of ordering in the

transition states.

C. Unimolecular Follow-Up Steps

Some p2ssible unimolecular follow-up steps have been discussedpreviously; these include (a) ring opening by $-cleavage reactions, andelimination of N-Nitroformimine (H2C-NNO2 ) from the ring-opened open-chainintermediates by further 3-cleavage reactions; and (b) further reaction ofH2 C=NN02 , most likely to give formaldehyde and N20 (both of which are known(see for example References 1, 7-9, 43, 44 and 51) to be formed in large

62C. E. Waring and G. Krastins, "The Kinetics and Mechanism of the Thermal

Decomposition of Nitroglycerin," J. Phys. Chem., Vol. 74, p. 999.. 1970.

63 R. A. Fifer, "A Hypothesis for the Phase Dependence of the Decomposition

Rate Constants of Propellant Molecules," in the abstract booklet for ONR-AFOSR-ARO Workshop on Fundamental Research Directions for the Decompositionof Energetic Materials. Berkeley, CA, January 1981.

64R. G. Coombes, "Nitro and Nitroso Compounds," D. Barton and W. D. Ollis,

ed., Comprehensive Organic Chemistry, Pergamon Press, Flmsford, NY. Vol. 2,

Chapter 7, p. 439, 1979.

65 G. M. Nazin, G. B. Manelis and F. I. Dubo itskii, "Thermal Decomposition of

Aliphatic Nitro-Compounds," Russ. Chem. Rev., Vol. 37, p. 603, 1968.

38

I /

amounts in HM and RDX decomposition), although at higher temperatures it ispossible that N-N cleavage of N-Nitroformimine to NO2 and H2CN might alsooccur.

D. Bimolecular Follow-up Steps

As discussed earlier,2 possible bimolecular follow-up steps include (a)abstraction of hydrogen from starting HMX and RDX by free radicals formed inthe reaction, and (b) attack on nitro oxygen by free radicals formed in thereaction, possibly followed by N-0 or N-N cleavage of the resultingoxynitroxide radical to give a nitrosoamine or a denitro nitrogen-centeredradical. Available literature analogies and thermo-chemical estimates 2 areconsistent with the idea that these are both reasonable follow-up steps.Possibly steps such as these, involving radicals formed either (a) directlyfrom HM or RDX decomposition or (b) by reaction between primary products suchas NO2 or H2 C=fO, are at least partly responsible for the high frequencyfactors and apparent autocatalysis of nitramine deconvposition referred toabove.

More work is needed on all aspects of HM and RDX decompositionmechanisms. While the above and similar mechanisms seem reasonable and,nnsistent to the present writer, the individual mechanisms are not firmly

itablished and in fact are at present best considered only as a basis forfurther discussion. The formation of other known products of HM and RDXdecomposition, such as N9 and NO, can be explained by adaptations orcombinations of the above mechanisms. Products such as 0), 02, and H20,

could be formed by reaction among primary products, for example NO2 and H11CO.

E. Extension to Combustion Conditions

Since combustion takes place at much higher temperatures and pressuresthan encountered in the low-temperature decomposition studies summarized here,it seems appropriate to discuss the possible effect of high temperature,pressure and heating rate. These have been discussed in our previouspresentation.2 Some further discussion follows.

When the decomposition takes place at increased pressure, there might bean increase in the importance of bimolecular processes relative tounimolecular processes; this might have an important effect on combustionbehavior, as discussed previously.2 Another possible effect of pressure mightbe that at sufficiently high pressures, the vapor phase might become socompressed that the environment "seen" by a single molecule might resemble aliquid more than a low-pressure vapor or gas; if this were the case thedecomposition mechanism might well resemble the liquid decomposition ratherthan a low-pressure gas; for modeling purposes, possibly, assumed activationenergies and frequency factors should be modified accordingly.

The effect of temperature on reaction mechanisms and products could alsobe imporLant; as temperature rises, reactions with high activation energywould be expected to accelerate relative to those with lower activationenergies, since the activation energy is simply the slope of a plot of rateconstant vs reciprocal temperature. Two examples of this have appearedearlier in the present report; these are the apparent temperature denendence

of the relative rate of N-NO2 cleavage and of HONO elimination in the gas-

39

ohase decomposition, 16 and the possible tendency for cleavage of H2C=NNO2 to

F1'CN and NO, to oecome more important relative to formation of N 20 and F 2 CO,a3 temperature rises. Such changes in relative importance of various chemicalmechanisms could give rise to temperature-and heating-rate-dependent changesin decomposition product distribution and chemistry; as with the pressureeffects, these might well be very important in modeling and understandingcombustion and explosive behavior.

Another possible effect of high heating rate or high temperature might beto cause the first step of the decomposition and unimolecular follow-up stepsto become faster relative to bimolecular follow-up steps because of the higheractivation energy characteristic of first-order reactions, and since more

unimolecular decomposition might be expected to take place immediately, withcorresponding decrease in opportunity for bimolecular follow-up steps

involving starting HMX or RDX molecules or early intermediates. This effectmight also cause important changes in product distribition or chemistry with

increasing temperature or heating rate. The temperature and pressure effectson the unimolecular/bimolecular ratio apparently work in opposite direction

but complete compensation is of course not assured.

In view of the preceding paragraphs, possibly the most useful aspect of

thermal decomposition studies at low temperatures and pressures is not to

provide product distributions and kinetic parameters that can be applied

directly to combustion conditions, but rather to e!Gcidate the types of

chemical decomposition processes involved, inc]uditg minor (at low

temperatures and pressures) pathways in addition to the principal ones.

Informed extension of this body of knowledge to combustion conditions couldthen provide the basis for improved understanding and control of combustion

processes and operational properties such as stability, sensitivity, and

burning rate behavior.

VI. WORK NFEDED

More work is needed In a number of areas. Several of these seemparticularly worth mentioning, among them the following:

1. The first step of the decomposition of W4X and RDY is still not wellunderstood. Tn addition to an improved understanding of the nature of thefirst step itself (for example, is it 1ONO elimination, N-NO2 cleavage, C-N

cleavage, or something else?) there is a need for a better understanding ofthe effect of temperature, pressure and state of aggregation (solid, liquid,vapor, as well as solvent effeg~s Time-resolved laser spectroscopic

techniques may be helpful here at least for the vapor-phase

decomposition.

668. H. Rockney and E. R. Grant, "Resonant Multiphoton Ionization Detection of

the NO2 Fragment from Infrared Multiphoton Dissociation of CH3NO'2 ," Chem.

Phys. Lett., Vol. 79, p. 15, 1981.

6 7K. E. Lewis, D. F. McMillen and D. M. Golden, "Laser-Powered HomogeneousPyrolysis of Aromatic Nitro Compounds," J. Phys. Chem., Vol. 84, p. 226,1980.

40

2. There seems to be very little work available on the gas-phasedecomposition of HIX and RDX. There Is a need for more understanding of thiswith regard to both the kinetics and the product distributions, especiallysince the gas-phase decomposition would most reflect the intrinsic behavior cthe molecules themselves; behavior in the liquid and solid phases could thenbe regarded as variations on the vapor-phase behevior, induced by theenvironment set up by neighboring molecules. In addition to techniques such

.X as those d scribed in References 16 and 66, laser-powered homogeneouspyrolysis 6' might well be capable of providing information on this point.Note that care should be taken to work under conditions such that the resultfare not influenced by wall reactions.

3. There is a need for improved understanding of the soli dphsedecompoiltion. In view of the discussions of Cosgrove and Oweng2 -4 and ofBatten, it seems clear that in studying the behavior of HMX and RDX belowtheir melting points, care should be taken to separate the true solid-statedecomposition from concurrent sublimation followed by gas-phase decompositioland to understand the relative roles of gas, liquid, and solid-statedecomposition: see the discussion on pages 31-35 of the present report.

4. There is also a need for improved understanding of the effect oftemperature and pressure on the decomposition of HMX and RDX. In extendinglow-temperature, low-pressure results to combustion conditions, it should beremembered that the Arrhenius parameters, which are usually used to carry outhese extensions, may themselves depend on temperature and pressure; improve(understending of these variations would enhance the reliability of theextension.

5. There is a need for improved understanding of the nature andoccurrence of autocatalysis and autoinhibition in the thermal decomposition 4HMX and RDX. This is especially true in view of apparent discrepancies

*between literature statements concerning acceleration or inhibition of HMX ai* RDX decom osition known products such as formaldehyde and oxides of

nitrogen. 4 4 ,4,49 , See also the discussion above under "Autocatalysis" an(references cited therein.

6. There is also a need for more research Into the effect of pressureHMX and RDX decomposition, With regard to both kinetics and productdistributions. One study, carried out at pressures up to 1000 psi (0.067kbar), resulted in activation energies for HMX decomposition which decreasedfrom 55.9 kcal/mole at atmospheric pressure to 418 kcal/mole at 1000 psi

*(0.067 kbar) of argon, although the activation energy for RDX decomposition

68D. F. Debenham and A. J. Owen, "The Thermal Decomposition of 1,3,5-

Trinitrohexahydro-1,3,5-triazine (iDX) In 1,3,5-Trinitrohenzene," Symp.Chem. Probl. Connected Stab. Explos. (Proc.), Vol. 4, p. 201, 1976., Pub.1977.

6 9D. A. Flanigan and B. B. Stokes, "HMX De lagration and Flame

Characterization. Volume I. Phase II Ni ramine Decomposition andDeflagration Characterization," Thiokol orporation, Huntsville Division,

" Huntsville, AL, Report AFRPL-TR-79-94, October 1980 (AD-B053 058L).

41

was reported to be independent of pressure from atmospheric pressure to 500psi (0.03 kbar). In a study of time-to-explosion versu,: cemperature for a

* number of explosives including HrX, 7 0) it was found that "activation energy"appeared constant from <1 kbar to 50 kba:; it was suggested that thedecomposition mechanism was independent of pressure. There has also been areport 17 that the activation energy for decomposition of RDX was ca 15kcal/mole lower when measured by closed-pan than by open-pan DSC. Pressureeffects on product distributions from HNX and RDX decomposition have beensummarized briefly.7 1 In view of the differences between experimentalconditions and results reported in these studies,'1 ,69- 7 1 it is clear thepressure effects on HMX and RDX decomposition are far from well understood,and much more work in this area is required.

VII. NOTES ADDED IN PROOF

A. Note Added in Proof No. I While this report was being proofread, theauthor became aware of a review article7 2 in the Russian literature; althoughas this is written this review probably will not be available in English

* translation for several months, it seems worth while to call it to theattention of anyone reading the present report.

B. Note Added in Proof No. 2 Brill and Karpowicz7 3 ,74 have recently*suggested that the decomposition reactions of condensed-phase HMX and RDX may*: be governed by release of intermolecular interactions occurring prior to. unimolecular decomposition, rather than by the decomposition steps" themselves. This is based on large (ca 40-50 kcal/mole) activation energies" observed for phase transitions among the solid polymorphic forms of HRX; Brill

aad Karpowicz feel that the large activation energies for these phasetransitions (much larger than the net energies of reaction for the sametransitions) represent energy needed for "freeing-up" of HMX or RDX molecules

70E. R. Lee, R. H. Sanborn and H. D. Stromberg, "Thermal Decomposition of High

Explosives at Static Pressures 10-50 Kilobars," Proceedings 5th Symposium(International) on Detonation, 1970, p.331-337, for sale by the Superintendent

o >:.of Documents, U.S. Government Printing Office, Washington, Dt 20402.71H. A. Schroeder, "Critical Analysis of Nitramine Decomposition Data:

Product Distributions from HMX and RDX Decomposition," Proceedings 18thJANNAF Combustion Meeting, Pasadena, CA, Vol. 2, p. 395, CPIA Publication347, October 19-23, 1981.

7 2F. I. Dabovitskii and B. L. Korsunskii, "Thermal Decomposition Kinetics of

N-Nitro Compounds," Usp. Khim., Vol. 50, p. 1828, 1981, cited ir, CurrentContents, Physical, Chemical and Earth Sciences, Vol. 22, p.144, No. 2,January 11, 1982.

73T. B. Brill and R. J. Karpowicz, "Solid Phase Transition Kinetics The Roleof Intermolecular Forces in the Condensed-Phase Decomposition of actahydro-1,3,5,7-tettanitro-1,3,5,7-tetrazocine," J. Phys. Chem., Vol. 86, p. 4260-5,1982.

74R. J. Karpowicz, L. S. Gelfand and T. B. Brill, "Application of Solid-PhaseTransition Kinetics to the Properties of HMX," AIAA Journal, Vol. 21,p. 310-12, 1983.

42

."%° - .- - .. .. .. -..-. ". . . . -*.° * ° .* . ..-.. . *- ,- .o.- - " . " -- .*- - - ". .- - - ° ° •.- - -

which presumably must take place before decomposition. The magnitudes of theenergies involved are such as to raise nt least the possibillty that thefreeing-up of the molecules may be the rate-determ.ning step, at least for thesolid-state decomposition.

Note that this treatment depends critically on the assumption that therate constants measured in References 73 and 74 and attributed to solid-solid

phase transitions in HMX, are actually rate constants for true first-orderprocesses and hence that the activation energies are also true activation

energies for a specific first-order process, not merely effective temperaturecoefficients of reaction (see Reference 24) for a complicated assembly ofprocesses.

In addition, Fifer 7 5 has published a more recent and accessiblediscussion than reference63 of the cage effect hypothesis. The basic idea of

this hypothesis is that the relative ordering of the rates and Arrheniusparameters for the gas, liquid and solid-state thermal decomposition ofnitramines and nitrate esters (Gas phase rates faster than liquid, which inturn are faster than solid-state rates of decomposition; Arrhenius parameters

* follow the opposite orlering) is explainable in terms of greater confinementof radicals (such as N and denitro-HMX/RDX) formed in the initial step ofdecomposition. This is in agreement with recent work76 on the thermolysis of1,2-diphenylethane.

Note that this hypothesis applies only to radical-producing reactions andnot, for example, to HONO elimination. However, even if the gas-phasereaction were found ultimately to proceed via some other mechanism, forexample HONO elimination, the cage-effect hypothesis might well still beuseful to understand quantitative differences between the observed liquid-phase decomposition kinetics and parameters, and values reliably estimated for

the hypothetical gas-phase radical pathways.

Furthermore it was argued 75 that a practical implication of the cageeffect hypothesis was that at higher temperatures the condensed phase rateswould approach those for the gas phase; so that at the higher temperaturecharacteristic of combustion it might be a reasonable approximation to use thegas phase kinetic parameters to represent the condensed phase decomposition.

The present writer suggests it may also be worthwhile to consider thepossibility that, at the higher pressures characteristic of combustion, the

density of the gas phase might be increased to the point where it mightresemble the liquid more than what would be thought of at more moderatepressures as a vapor: if this is true, the system might exhibit behavior suchthat it would be the vapor phase that would assume Arrhenius parameters

characteristic of the liquid, rather than the other way around.

7 5 R. A. Fifer, "Cage Effects in the Thermal Decomposition of Nitramines andOther Energetic Materials," Proceedings 19th JANNAF Combustion heeting,Greenbelt, MD; Vol. I, CPIA Publication 366, p. 311-319, October 1982.

S76. E. Stein, D. A. Robaugh, A. D. Alfieri and R. E. Miller, "Bond Homolysis

in High-Temperature Fluids," J. Amer. Chem. Soc., Vol. 104, p. 6567-70,

1982.

43

At the very least, both of the effects7 3- 76 described in the aboveparagraphs will have to be better understood than at present before Arrheniusparameters applicable to combustion conditions can be reliable derived fromstudies of decomposition under more moderate temperatures and pressures. Itwill also of course be necessary to understand the role of such factors asdielectric constant of the medium, and other types of solvent effects andintermolecular interactions.

C. Note Added in Proof No. 3 It also seems worthwhile to mention aninteresting paper in which Burov and Nazin 7 7 have very recently reported somekinetic measurements on gas phase thermal decomposition of several nitraminesincluding HMX and RDX. Other compounds studied included N,N-dinitropiperazineand 1,3-dinitrazacyclopentadiene. The decompositions of all of thesecompounds except HMX were studied in the presence of NO, addition of whichnoticeably affected the kinetics, resulting in lower rates by factors of 2 to4 at 200*C, as well as noticeable changes in Arrhenius parameters; thus chainreactions or autocatalysis are apparently of some importance here. Thedecompositions were studied manometrically, at pressures of 0.05-0.1 mm Hg.Gas phase and solution kinetic measurements on the above nitramines as well asdimeth l and diethyl nitramines and N-nitropiperidine were summarized in atable.7

The authors7 7 make the interesting suggestion that differences indecomposition rates of these nitramines are determined by the configuration ofthe amino nitrogens, the more-rapidly decomposing, low-activation-energy

*' compounds, including RDX, being those with tetrahedral or pyrimidal nitrogens,whil the slower-decomposing, higher activation energy compounds have trigonal

. coplanar nitrogens. This will be discussed further in a final, wrap-upportion of the present revisw, which will be devoted to chemical and physicalmechanisms of decomposition.

It also seems worth mentioning that the authors of Reference 77 are ofthe opinion that the N-NO bond dissociation energy of nitromethane is about40 kcai/mole, giving as teir authority a Russian book78 which, as far as thepresent writer is aware, is not available in English translation. This value

Iis considerably lower than the 46.2 kcal/mole estimated by Shaw and Walker fordimethylnitramine and applied also to HMX. Korsunskii and Dubovitskii7 2 alsoseein to feel that the N-NO2 bond dissociation energy for simple nitramines isaround 40 kcal/mole. This discrepancy should be checked into further, in viewof the obvious importance of an accurate knowledge of the N-N02 dissociationenergies of dimethylnitramine and other nitramines to the decompositionchemistry of these compounds. In view of the possible importance of wallreactions and autocatalysis, and of decomposition pathways such as HONO

77yu. M. Burov and G. H. Nazin, "Influence of Structure on Rate ofDecomposition of Secondary Nitramines in the Gas Phase," Kinetika i Kataliz,Vol. 23, No. 1, pp. 12-17, 1982 (English Translation, p. 5-10).

78L. V. rurvich, G. V. Karachevtsev, V. N. Kondrat'ev, Yu. A. Lebedev,V. A. Dedvedev, V. K. Potapov and Yu. S. Khodeev, "Chemical Bond RuptureEnergy, Ionization Potentials and Electron Affinity," Nauka, Moscow, 1974,(Reference 15 of reference 77 above).

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4

elimination, this knowledge should be obtained from sources, such asthermochemical studies, that are independent of kinetic measurements on thedecomposition reactions of the nitramines.

It seems worth noting that Reference 77 says that Shaw and Walker'sestimated parameters for N-NO2 bond dissociation were taken from a privatecommunication concerning DMNA. The value of E was stated to have been adopted

. without change, and log A to have been multiplied by 4. However, anexamination of Shaw and Walker's paper (Reference 27 of the present report)

shows that they are based on heats of formation and frequency factors given inReferences 12-14 and 21 of Reference 27 of the present report; thesereferences are not to any private communications but to two journal articlesand to two standard compilations of data* In particular the 7- NO2

dissociation energy is based on, in addition to (CH3)2 NN(v2, heats offormation for (CH) 2 N" and NO , which are the same as those given in standardcompilations of data.8 '8 Slaw and Walker also cite a number of reported

ovalues for the N-NO2 bond dissociation energy, nearly all of which are higherthan 40 kcal/mole, ranging from 47 to 66 kcal/mole. Thus the 46.2 kcal/moleestimated by Shaw and Walker for the N-NO2 dissociation energy ofdimethylnitramine seems to be reasonably well-founded in the literature.77

* However it would be most helpful to have access to the reference cited assupporting an upper limit of 170 kJ/mole (40.6 kcal/mole) for the N-N02 bond

* energy of dimethylnitramine; expecially since additional measurements mightlead to revision of the heats of formation on which the figure of 46.2kcal/mole ws based. The frequency factor (log A - 15.8) suggested by Shawand Walker2 was based on an average of values from decomposition ofnitromethane and N204 ; possibly more elaborate thermochemical calculationswould be helpful in arriving at a firmer value.

Activation energies and frequency factors (log A(sec-1 )) reported inReference 77 were as follows: for RDX, 146.6 kJ/mole (35.04) kcal/mole) and13.5 without NO; 167.6 kJ/mole (40.06 kcal/mole) (see footnote, p. 6 ofReference 77) and 15.6 with NO. For HKX, the values were 165.5 kJ/mole(39.56) kcal/mole) and 14.2 without added NO. N,N'-dinitropiperazine gave 160kJ/mole (38.2 kcal/mole) and 13.6 alone, but 151.2 ki/mole (36.14 kcal/mole)and 12.0 in the presence of NO, while 1,3-dinitrazacyclopentane gave 146.6kJ/mole (35.04 kcal/mole) and 13.5 alone and 169.3 kJ/mole (40.46) kcal/mole)and 15.6 in the presence of NO.

When the results for RDX are plotted alongaide those given in Figure 2,they do not fall on the same line as the other results plotted in Figure 2,

7 9R. C. Cass, S. E. Fletcher, C. T. Mortimer, P. G. Quincey and H. D.Springall, "Heats of Combustion and Molecular Structure, Part IV. AliphaticNitroalkanes and Nitric Esters," J. Chem. Soc., p. 958-63, 1958.

8 0R. C. Weast and M. J. Astle, eds., CRC Handbook of Chemistry and Physics,

p. F-204, 63rd. edition, CRC Press, Inc.', Boca Raton, FL, 1982-1983.

_81S. W. Benson, "Thermochemical Kinetics," 2nd. edition, Wiley, New York, NY,1976, p. 292.

45

but lie on a parallel line, about 0.5 log unit below those plotted in thefigure. However, they no not seem to fit the other points on the graph aswell as the data of Belyaeva et al., judging from the degree of scatter whenthe line defined by the points of Reference 77 is extended through the otherpoints.

There also seems to be a series of typographical errors in Table 1,column 6 of Reference 77; the values given do not mata those calculated fromthe values of E and log A (sec -1 ) in columns 4 and 5. The present writerrecalculated the numbers in column 6 of Table I of reference7 7 and obtainedthe following values: line 1, 0.268 instead of 4; line 2, 1.67 instead of0.158; line 3, 5.0 instead of 0.525; line 4, 721 instead of 0.676; line 5,2.12 instead of 0.2; line 6, 31.2 instead of 2.9; line 7, 22.5 instead of2.24; line 8, 8.73 instead of 0.87; line 9, 530 instead of 50; line 10, 666instead of 63; line 11, 207 instead of 20; line 12, 81.3 instead of 8; line13, 1.7 instead of 0.56; line 14, 5.20 instead of 0.56; line 15, 255 insteadof 2500; line 16, 8.50 instead of 0.8; line 17, 0.631 instead of 0.063; line18, 8.64 instead of 0.83; line 19, 2.03 instead of 0.22; line 20, 24.5 insteadof 2.5; line 21, 207 instead of 20; line 22, 81.3 instead of 8.

I4

* I

/4

//

/ ACKNOWLEDGEMENTS/"

/ The author is most grateful to the following for providing help anddiscussions in the course of this work: R. J. Powers and J. Whidden, AirForce Armament Test Laboratory; G. A. Lo and T. E. Sharp, Lockheed Palo A.co

Research Laboratory; D. F. McMillen, D. M. Golden, D. R. Crosley andJ. R. Barker, SRI International; B. B. Goshgarian, W, E. Roe and F. Goetz, Air

Force Rocket Propulsion Laboratox.,; D. A. Flanigan, W. H. Graham andJ. W. Blamks, Thiokol, Huntsville; K. P. McCarty, Hercules, C. L. Coon,R. R. McGuire and C. M. Tarver, Lawrence Livermore Laboratories; J. Janney nnd

R. N. Rogers, Lor Alamos Scientil-c Laboratory; R. A. Beyer, R. A. Fifer,E. Freedman, J. M. Heimerl, T. P. Coffee, G. E. Keller, J. P. Pftu,J. J. Rocchio, A. A. Juhasz, R. A. Wires, S. Wise, M. S. Miller, and A. Cohen,

Ballistic Research Laboratory; G.W. Nauflett and M. J. Kamlet, Naval SurfaceWeapons Center; E. R. Grant, Cornell University; T. B. Rrill, University of

Delaware; Suryanarayana Bulusu, LCWSL; C. F. Rowell, U. S. Naval Academy:

H. L. Pugh and L. P. Davis, USAFSRL: E. C. Janzen, University of Cuelph;K. Kraeutle, Naval Weapons Center; M. BenReuven, Princeton Combustion ResearchLaboratories; H. N. Volltrauer. Aerochem Research Laboratories: and RobertShaw.

The author thanks E. Freedman, BRL, for calling attention to Reference24; J. M. Heimerl, BRL for calling attention to the statistical treatment inreferences 25 and 26; and to J.M. Heimerl, C. E. Keller and T. P. Coffee (allof BRL) for generous assistance with the statistical analysis and for

furnishing copies of the programs used.

The author is especially grateful to R. N. Rogers, Los Alamos National

Laboratories, R. J. Powers, (AFATL), Eglin AFB, Florida and D. F. McMillen,SRI International for furnishing unpublished rai data for statistical

analysis. The data furnished by Dr. McMillen was obtained in the course ofwork supported by the U.S. Department of Energy through Lawrence LivermoreLaboratories.

47

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14. R. N. Rogers and G. W. Daub, "Scanning Calorimetric Determination ofVapor-Phase Kinetic Data," Anal. Chem., Vol. 45, p. 596, 1979.

15. P. J. Robinson and K. A. Holbrook, "Unimolecular Reactions," Wiley-Interscience, New York, pp. 6-7, 1972.

16. D. F. McMillen, J. R. Barker, K. E. Lewis, P. L. Travor andD. M. Golden, "Mechanisms of Nitramine Decomposition: Very-Low PressurePyrolysis of HNX and Dimethylnitramine," Final Report, SRI Project PYU-5787, 18 June 1979 (SAN 0115/117). Supported by Department of Energythrough Lawrence Livermore Laboratories.

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* Explosives, Vol. 2, p. 78, 1977.

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19. J. H. Sharp, "Differential Thermal Analysis," R. C. Mackenzie, ed.,Vol. 2, Chapter 28, see especially p. 55, Academic Press, New York, NY,1972.

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25. R. J. Cvetanovic and D. L. Singleton, "Comment on the Evaluation of theArrhenius Parameters by the Least Squares Method," Int. J. Chem. Kinet.,Vol. 9, p. 481, 1977.

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27. R. Shaw and F. E. Walker, "Estimated Kinetics and.Thermochemistry ofSome Initial Unimolecular Reactions in the Thermal Decomposition of1 ,3,5,7-Tetranitro-1,3,5,7-tetraazacyclooctane in the Gas Phase," 3.Phys. Chem. Vol. 81, p. 2572, 1977.

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30. B. L. Korsunskii, F. I. Dubovitskii and E. A. Shurygin, "Kinetics of theThermal Decomposition of N-N-Diethylnitroamine and M&Nitropiperidine,"Izvest. Akad. Nauk. SSSR, Ser. Khim., p. M42, (Eng. Transl. p. 1405)1967.

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35. F. I. Dubovitskii, Yu. I. Ruhtsov, V. V. Barykin and G. B. Manelis,"Kinetics of Thermal Decomposition of Diethylnitramine Dinitrate," Bull.Acad. Sci. USSR, Div. Chem. Sci., p. 1126, 1960.

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39. B. L. Korsunskii, L. Ya. Kiseleva, V. I. Ramushev and F. I. Dubovitskii,"Kinetics of the Thermal Decomposition of bis-(2,2-Dinitropropyl)-N-nitroamine," Izv. Akad. Nauk. SSSR, Ser. Khim, P. 1778, (Eng. Transl.,p. 1699) 1974.

39. G. V. Sitonin, B. L. Korsunskii, N. F. Pyamakov, Yo G. Shvaiko,I. Sh. Abrakhmov and F. I. Dubovitskii, "The Kinetics of the ThermalDecomposition of N, N-Dinitropiperazine and 1,3-Dinitro-l,3-Diazacyclopentane," Izv. Akad. Nauk. SSSR, Ser Khim., p. 311, (Eng.Transl., p. 284) 1979.

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40. W. P. Colman and F. C. Rauch, "Studies on Composition B," Final Report,Contract No. DAAA21.70-0531, American Cyanamid Company, February 1971(AD-381 190).

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51

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53. J. N. Bradley, A. K. Butler, W. D. Capey and J. R. Gilbert, "MassSpectrometric Study of the Thermal Decomposition of 1,3,5-Trinitohexahydro-1,3,5-triazine (RDX)," J. Chem. Soc., Faraday Trans.Pt. 1, Vol. 73, p. 1789, 1977.

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55. R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energieswith a Differential Scanning Calorimeter," Anal. Che ., Vol. 38, p. 412,1966.

56. P. G. Hall, "Thermal Decomposition and Phase Transitions in SolidNitramines," J. Chem. Soc., Faraday Trans. Pt. 2, Vol. 67, p. 556, 1971.

57. B. V. Novazhilov, "The Temperature Dependence of the Ki-eticCharacteristics of Exothermic Reactions in the Condensed Phase," Dokl.Akad. Nauk. SSSR, Vol. 154, p. 106, 1964.

58. B. L. Korsunskii, F. I. Dubovitskii and G. V. Sitonina, "Kinetics of theThermal Decomposition of N,N-Dimethylnitroamine in the Presence ofFormaldehyde," Dokl. Akad. Nauk. SSSR, Vol. 174, p. 1126, (Eng. Transl.,

p. 436) 1967.

59. S. W. Benson and H. E. O'Neal, "Kinetic Data on Gas-Phase UnimolecularReactions," NSRDS-NBS 21, p. 314ff. For sale by the Superintendent ofDocuments, US Printing Office, Washington, DC 20402, February 1970.

60. S. W. Benson, "Thermochemical Kinetics," Wiley Interscience, New York,p. 117, 1976.

61. B. Suryanarayana, R. J. Graybush and J. R. Autera, "Thermal Degradationof Secondary Nitramines: A Nitrogen-15 Tracer Study of HMX (1,3,5,7-Tetranitro-1,3,5,7-Tetrazacyclooctane)," Chem. Ind., London, 2177, 1967.

62. C. E. Waring and G. Krastins, "The Kinetics and Mechanism of the ThermalDecomposition of Nitroglycerin," J. Phys. Chem., Vol. 74, P. 999., 1970.

63. R. A. Fifer, "A Hypothesis for the Phase Dependence of the DecompositionRate Constants of Propellant Molecules," in the abstract booklet forONR-AFOSR-ARO Workshop on Fundamental Research Directions- for theDecomposition of Energetic Materials, Berkeley, CA, January 1981.

64. R. G. Coombes, "Nitro and Nitroso Compounds," D. Barton and W. D. Ollis,ed., Comprehensive Organic Chemistry, Pergamon Press, Elmsford, NewYork, Vol. 2, Chapter 7, p. 439, 1979.

65. G. M. Nazin, G. B. Manelis and F. I. Dubovitskii, "Thermal Decompositionof Aliphatic Nitro-Compounds," Russ. Chem. Rev. Vol. 37, p. 603, 1968.

66. B. H. Rockney and E. R. Grant, "Reonant Multiphoton IonizationDetection of the NO2 Fragment from Infrared Multiphoton Dissociation ofCH3 NO2 ," Chem. Phys. Lett., Vol. 79, p. 15, 1981.

52

67. K. E. Lewis, D. F. McMillen and D. M. Goiden, "Laser-Powered HomogeneousPyrolysis of Aromatic Nitro Compounds," J.. Phys. Chem., Vol. 84, p. 226,1980.

68. D. F. Debenham and A. J. Owen, "The Thermal Decomposition of 1,3,5-Trinitrohexahydro-1,3,5-triazine (RDX) in 1,3,5-Trinitrobenzane," Symp.Chem. Probl. Connected Stab. Explos. (Proc.), Vol. 4, p. 201, 1976.,Pub. 1977.

- 69. D. A. Flanigan and B. B. Stokes, "HMX Deflagration and FlameCharacterization. Volume I. Phase II Nitramine Decomposition andDeflagration Characterization," Thiokol Corporation, HuntsvilleDivision, Huntsville, AL, Report AFRPL-TR-79-94, October 1980 (AD-B053058L).

70. E. R. Lee, R. H. Sanborn and H. D. Stromberg,"Thermal Decomposition ofHigh Explosives at Static Pressures 10-50 Kilobars," Proceedings 5thSymposium (International) on Detonation, 1970, p. 331-337, for sale bythe Superintendent of Documents, U.S. Government Printing Office,Washington, DC 20402.

71. M. A. Schroeder, "Critical Analysis of Nitramine Decomposition Data:Product Distributions from HMX and RDX Decomposition," Proceedings 18thJANNAF Combustion Meeting, Pasadena, CA, Vol. 2, p. 395, CPIAPublication 347, October 19-23, 1981.

72. F. I. Dubovitskii and B. L. Korsunskii, "Thermal Decomposition Kineticsof N-Nitro Compounds," Usp. Khim., Vol. 50, p. 1828, 1981, cited inCurrent Contents, Physical, Chemical and Earth Sciences, Vol. 22, p.144, No. 2, January 11, 1982.

73. T. B. Brill and R. J. Karpowicz, "Solid Phase Transition Kinetics TheRole of Intermolecular Forces in the Condensed-Phase Decomposition ofOctahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine," J. Phvs. Chem.,Vol. 86, pp. 4260-5, 1982.

74. R. J. Karpowicz, L. S. Gelfand and T. B. Brill, "Application of Solid-Phase Transition Kinetics to the Properties of HMX," AIM Journal.,Vol. 21, pp. 310-12, 1983.

75. R. A. Fifer, "Cage Effects in the Thermal Decomposition of Nitraminesand Other Energetic Materials," Proceedings of the 19th JANNAFCombustion Meeting, Greenbelt, MD; October 1982, Vol. 1, CPIAPublication 366, pp. 311-319.

76. S. E. Stein, D. A. Robaugh, A. D. Alfieri and R. E. Miller, "BondHomolysis in High-Temperature Fluids," J. Amer. Chem. Soc., Vol. 104,pp. 6567-70, 1982.

77. Yu. M. Burov and G. M. Nazin, "Influence of Structure on Rate ofDecomposition of Secondary Nitramines in the Gas Phase," Kinetika iKataliz, Vol. 23, No. 1, pp. 12-17, 1982 (Eng. Transl., pp. 5-10).

53

78. L. V. Gurvich, G. V. Karachevtsev, V. N. Kondrat'ev, Yu. A. Lebedev,V. A. Dedvedev, V. K. Potapov and Yu. S. Khodeev, "Chemical Bond RuptureEnergy, Ionization Potentials and Electron Affinity," Nauka, Moscow,1974, (Reference 15 of reference 77 above).

79. R. C. Cass, S. E. Fletcher, C. T. Mortimer, P. G. Quincey dndH. D. Springall, "Heats of Combustion and Molecular Structure, Part IV,Aliphatic Nitroalkanes and Nitric Esters," J. Chem. Soc., pp. 958-63,1958.

80. R. C. Weast and M. J, Astle, eds., CRC Handbook of Chemistry andPhysics, 63rd edition, 1982-1983, CRC Press, Inc., Boca Raton, Florida,p. F-204.

81. S. W. Benson, Thermochemical Kinetics" 2nd Edition, Wiley, New York, NY,1976, p. 292.

A-i R. N. Rogers and G. W. Daub, "Scanning Calorimetric Determination of

Vapor-Phase Kinetics Data," Anal. Chem., Vol. 45, p. 596, 1973.

A-2 D. F. McMillen, J. R. Barker, K. E. Lewis, P. L. Trevor andD. M. Golden, "Mechanisms of Nitramine Decompositions: Very Low-Pressure Pyrolysis of HMX and Dimethylnitramine," Final Report on SRI

Project PYU 5787, Supported by Department of Energy through LawrenceLivermore Laboratories, Contract No. EY-76-C-03-0115, 18 June 1979.

A-3 M. S. Belyayeva, G. K. Klimenko, L. 1. Babaytseva, P. N. Stolyarov,"Factors Determining the Thermal Stability of Cyclic Nitramines in theCrystalLine State," FTi-ID(RS)T-1209-78 (AD-B033 572L).

A-4 R. M. Potter, G. J. Knutson, and M. F. Zimmer, Compat. PropellantsExplos. Pyrotechnics Plast. Addit., Conf. Pub. 1975, 1I-D., 12 pp.,Chem. Abstr., Vol. 86, 14411j, 1974.

B-i A. J. B. Robertson, "The Thermal Decomposition of Explosives. Part IICyclotrimethylenetrinitramine and Cyclotetramethylenetetranlitramine,'"Trans. Faraday Soc., Vol. 45, p. 85, 1949.

B-2 R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energies-with a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p. 412,

1966.

B-3 R. N. Rogers and L. C. Smith, "Estimation of Preexponential Factor fromThermal Decomposition Curve of an Unweighed Sample," Anal. Chem.,Vol. 39, p. 1024, 1967.

B-4 E. ". Rideal and A. J. B. Robertson, "The Sensitiveness of Solid High

Explosives to Impact," Proc. Roy. Soc., Vol. 195A, p. 135, 1948.

B-5 R. N. Rogers, "Differential Scarning Calorimetric Determination ofKinetic Constants of Systems that Melt with Decomposition,"Thermochimica Acta, Vol. 3, p. 437, 1972.

I

B-6 B. B. Goshgarian, "The Thermal Decomposition of Cyclotrimethylene-trinitramine (RDX) and Cyclotecramethylenetetranitramine (HMX)," AFRPL-TR-78-76 (AD-B032 275L).

B-7 D. A. Flanigan and B. B. Stokes, "HMX Deflagration and FlameCharacterization. Volume I. rase II Nitramine Decomposition andDeflagration Characterization," Thiokol Corporation, HuntsvilleDivision, Huntsville, AL, Report AFRPL-TR-79-94, October 1980 (AD-B053058).

B-8 R. J. Powers, "Hezards Due to Precombustion Behavior of High EnergyPropellants," AFATL, Private Communication, June 1980, of data presenteat JANNAF Workshop, Eglin AFB, April 1980.

B-9 Yu. Ya. Maksimov, "Thermal Decomposition of Hexagen and Octogen," Tr.Mosk. Khim-Tekhnol, Inst. No 53, p. 73, 1967; see Chem. Abstr., Vol. 68p. 41742r. Translated by H. J. Dahlby, Los Alamos Report LA-TR-68-30,Los Alamos, 1968.

B-10 Maksimov (presumably), work summarized in K. K. Andreyev, "ThermalDecomposition and Combustion of Explosives," FTD-HT-23-1329-68, p. 87,p. 130 (AD-693 600).

B-11 R. N. Rogers, Los Alamos Scientific Laboratories, Private Communicatio,February 1980.

C-I A. J. B. Robertson, "The Thermal Decompositon of Explosives. Part II.Cyclotrimethylenetrinitramine and Cyclotetramethylenetetranitraminr,"Trans. Faraday Soc., Vol. 45, p. 85, 1949.

-"C-2 A. J. B. Robertson, S.A.C. No. 4885, referred to in Reference 5.

C-3 G. K. Adams, S.A.C. No. 5766, "The Thermal Decomposition of RDX,"February 1944.

C-4 A. 3. B. Robertson, S.A.C. No. 3264, referred to in Reference 5.

C-5 J. Wilby, "Thermal Decomposition of RDX/TNT Mixtures, Part I," A.R.D.EReport (MX) 16/59, AD-225 991, August 1959.

--C-6- C. E. H. Pawn, J. K. Hays and F. H. Pollard, "The Thermal Decompositioof Tetryl and RDX," S.A.C. No. 2025, April 1942.

C-7 A. J. B. Robertson and R. P. Sinclair, "The Thermal Sensitivity ofExplosives," S.A.C. No. 1596, January 1942.

C-8 F. C. Rauch and R. B. Wainwright, "Studies on Composition B," FinalReport, Contract No. DAAA21-68-C-0334, American Cyanamid Company,Febraury 1969, AD-850 928.

C-9 F. C. Rauch and A. J. Fanelli, "The Thermal Decomposition Kinetics ofHexahydro-1,3,5-trinitro-s-triazine above tte Milting Point: Evidencefor Both a Gas and Liquid-Phase Decomposition," J. Phys. Chem. Vol. 73

p. 1604, 1969.

I5

o,7

C-10 F. C. Rauch and W. P. Colman, "Studies on Composition B." Final Report,Contract No. DAAA 21-68-C-0334, American Cyanamid Company, March 1970,AD-869 226.

C-I R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energieswith a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p..412,

1966.

C-12 R. N. Rogers and L. C. Smith, "Estimation of Preexponential Factor fromThermal Decomposition Curve of an Unweighed Sample," Anal. Chem.,

Vol. 39, pp. 1024-5.

C-13 R. N. Rogers and G. W. Daub, "Scanning Calorimetric Determination ofVapor-Phase Ki.netics Data," Anal. Chem., Vol. 45, p. 596, 1973.

C-14 R. N. Rogers, "Determination of Condensed-Phase Kinetics Constants,"Therochimica Acta, Vol. 9, p. 444, 1974.

C-15 P. G. Hall, "Thermal Decompositiaon and Phase Transitions in Solid

Nitramines," J. Chem. Soc., Faraday Trans., Part II. Vol. 67, p. 556,1971.

C-16 K. Kishore, "Thermal Decomposi -o- Studies on Hexahydro-1,3,5-trinitro-s-triazene (RDX) by Differentii. eanning Calorimetry," Propellants and

- Explosives, Vol. 2, p. 78, 1978.

* C-17 T. B. Joyner,"Thermal Decomposition of Explosives. Part I. Effect ofAsphalt on the Decomposition of Asphalt-Bearing Explosives," NWC TP4709, March 1969, AD-500 573.

C-18 J. Harris, "Autoignition Temperatures of Military High Explosives byDifferential Thermal Analysis," Thermochimica Acta, Vol. 14, p. 183,1976.

C-19 J. Harris and E. Demberg, "Autoignition Temperatures of Military High

Explosives by Differential Thermal Analysis," PATR 4481, March 1973, AD-

908 846L.

C-20 T. G. Floyd, "Reaction Kinetics of Temperature-Cycled Cyclotrimethylene-trinitramine (RDX)," Journal of Hazardous Materials, Vol. 2, p. 163,

1977/78.

C-21 W. P. Colman and F. C. Rauch, "Studies on Composition B," Final Report,Contract No. DAAA21-70-0531, American Cyanimid Company, February 1971.,AD-881 190.

C-22 J. Wilby, "Thermal Decomposition of RDX/TNT Mixtures, Part I.," A.R.D.E.Report (MX) 16/59, August 1959, AD-225 991.

C-23 J. Wilby, "Thermal Stability of RDX and HMX Compositions, Particularlytheir Mixtures with TNT," Symp. Chem. Probl. Connected Stab. Explos.,(Proc.), pp. 51-65, 1967, for availability see Reference C-24, 1968.

56

.............. ..... ,- ........................... .

C-24 D. F. Debenham and A. J. Owen, "The Thermal Decomposition of 1,3,5-trinitro-hexahydro-1,3,5-triazine (RDX) in 1,3,4-Trinitrobenzene," Symp.Chem. Probl. Connected Stab. Explos., (Proc.) 1976 (Pub. 19'7) Vol. 4,pp. 210-20; can be ordered from the Secretary, Tekn Lic Stig Johansson,Sektionen for Detonik och Forbranning, Box 608, S-551 02 Jonkoping,Sweden. Postal Account No. 507690-6, Banking Account Gotabanken No. 652-4383.

C-25 Yu. Ya. Maksimov, "Thermal Decomposition of Hexogen and Octogen," Tr.Mosk. Khim.-Tekhnol, Inst. No. 53, p. 73, 1967, see Chem. Abstr.,Vol. 68, p. 41742r., Translated by H. J. Dahlby, Los Alamos ScientificLaboatory Report LA-TR-68-30, Los Alamos, NM, 1968.

C-26 Maksimov (Presumably), work summarized in K. K. Andreyev, "ThermalDecomposition and Combustion of Explosives," FTD-HT-23-1329-68, p. 87,p. 130 (AD-693 600).

C-27 K. K. Miles, "The Thermal Decomposition of RDX," Master's Thesis, NavalPostgraduate S-"ool, Monterey, CA, (AD-743 762) March 1972.

C-28 D. A. Flanigan and B. B. Stokes, "HMX Deflagration and FlameCharacterization. Volume I. Phase II Nitramine Decomposition andDeflagration Characterization," ThLokol Corporation, HuntsvilleDivision, Huntsville, AL, Report AFRPL-TR-79-94, October 1980 (AD-B053058L).

C-29 R. M. Potter, G. J. Knutson, and M. F. Zimmer, "Effect on Dibutyl TinDilaurate on the Thermal Decomposition of RDX," Compat. Propellants,Explos. Pyrotechnics Plast. Addit., Conf. 1974, II-D, 1975.

C-30 K. Kishore, "Comparative Studies on the Decomposition Behavior ofSecondary Explosives RDX and HMX," Defense Science Journal, Vol. 18,p. 59, 1978, summarized in Chem. Abstr., Vol. 90, 206758v.

C-31 P. W. M. Jacobs and A. R. T. Kureishy, J. Chem. Soc., p. 4781, 964.

. D-1 B. B. Goshgarian, "The Thermal Decomposition of Cyclotrimethylene-trinitramine (RDX), and Cyclotetramethylenetetranitramine (HMX)," AFRPL-TR-78-76, October 1978 (AD-B032 275L).

D-2 Yu. Ya. Maksimov, "Thermal Decomposition of Hexogen and Octogen," Tr.- Mosk. Khim.--Takhnol., Inst. No. 53, p. 73, see Chem. Abstr., Vol. 68,

" p. 41742r, Translated by H. J. Dahlby, Los Alamos Report LA-TR-68-30,Los Alamos, NM, 1968.

D-3 Maksimov, work summarired in K. K. Andreyev, "Thermal Decomposition andCombustion of Explosives," FTD-HT-23-1329-68, p. 87, 130 (AD-693 600).

D-4 G. K. Adams, "Chemistry of the Solid State," personal communicationreferred to by C. H. Bawn, W. H. Garner, ed., Butterworths, London,p. 265, 1955.

D-5 G. K. Adams, "The Thermal Decomposition of RDX," S. A. C. 5766,1 February 1944.

57

U

* - - *- - - .+ . - * - %* * .-

. D-6 C. E. H. Bawn, in "Chemistry of the Solid State," W.E. Garner, ed.,Butterworths, London, p. 261, 1955.

D-7 J. J. Batten and D. C. Murdie, "The Thermal Decomposition of RDX atTemperatures Below the Melting Point. II. Activation Energy," Aust. J.

Chem., Vol. 23, p. 749, 1970.

D-8 J. J. Batten "The Thermal Decomposition of RDX at Temperatures Eelow theMelting Point. IV. Catalysis of the Decomposition by Formaldehyde,"

Aust. J. Chem., Vol. 24, pp. 2025-9, 1971.

D-9 K. K. Miles, "The Thermal Decomposition of RDX," Master's Thesis, USNaval Postgraduate School, Monterey, CA, March 1972 (AD-743762).

" D-10 P. G. Hall, "Thermal Decomposition and Phase Transitions in Solid

Nitramines," J. Chem. Soc., Faraday Trans. Part 2, Vol. 67, p. 556,1971.

" D-11 A. E. Medvedev, G. V. Sakovi,_h, and V. V. Konstantinov, "NonisothermalKinetics of the Solid-phase Decomposition of Octogen," Tezisy Dokl.Sovesch. Kinet. Mekh. Khim. Reakts. Tverd. Tele., 7th., Vol. 1,

pp. 163-5, 1977, Chem. Abstr., Vol. 88, p. 177810g, 1978.

D-12 R. R. Miller, R. C. Musso, and A. F. Grigor, "Combustion Mechanisms ofLow Burning Rate Propellant," AFRPL-TR-69-130, May 1969 (AD-502957).

D-13 S. (sic) Goshgarian, private communication cited in K. P. McCarty, "HKXPropellant Combustion Studies," AFRPL-TR-76-59 (AD-BO17 527L).

D-14 W. Hoondee, "The Thermal Decomposition of 8-HMX," Master's Thesis, NavalPostgraduate School, Monterey, CA, June 1971 (AD-728 582).

D-15 J. E. Sinclair and W. Hoondee, "The Thermal Decomposition of 0-HMX,"Proc. Symp. Explos. Pyrotechnics, 7th, 1-5, 1-4, 1971 (Chem. Abstr.,

Vol. 76, 143050w).

D-16 J. N. Haycock and V. R. Pai Verneckei, "Thermal Decomposition of 0-HMX(Cyclotetramethylene Tetranitramine) ," Explosivestoffe, Vol. 17, p. 5,1969.

D-17 B. Suryanarana and R. J. Graybush, "Thermal Decomposition of 1,3,5,7-Tetranitro-1,3,5,7-Tetreazacyclooccane (HMX): A Mass SpectrometricStudy of the Products from 8-HMX," Ind. Chim. BeIg., Vol. 32, Spec. No.

Part 3, pp. 647-50, 1967.

D-18 B. Suryanarayana, V. I. Siele, and J. Harris, unpublished work cited inReference 19.

D-19 B. Suryanarayana, J. R. Autera, and R. J. Graybush, "Mechanism ofThermal Decomposition of HMX (1,3,5,7-Tetranitro-1,3,5,7-Tetraazic~clo-octane)," Proceedings of the 1968 Army Science Conference, (OCRD) WestPoint, Vol. 2, p. 423, 1968 (AD-837 173).

58

/

1?.

D-20 J. E. Sinclair and W. Hoondee, "Thermal Decomposition of 8-HMX,"Jahrestag, Inst. Chem. Treib., Explosivestoffe Fraunhofer-Ges. 1971,Pub. 1972, 57, Chem. Abstr., Vol.81, 108070J.

D-21 R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energieswith a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p. 412,1966.

D-22 M. S. Belyayeva, G. K. Klimenko, L. T. Babaytseva, and P. N. Stolyarov,"Factors Determining the Thermal Stability of Cyclic Nitroamines in theI Crystalline State," FTD-iD(RS)T-1209-.78, AD-B033 572L.

D-23 J. Kimure and N. Kubota, "Thermal Decomposition Process of HMX,"Propellants and Explosives, Vol. 5, p. 1, 1980.

D-24 K. Takaira and K. Okazaki, M.S. Thesis, 1974, National Defense Academy,4cited in Reference 23.

. D-25 B. Goshgarian, Private Communication, August 1976, cited in Reference23.

D-26 M. Farber and R. D. Srivastava, "A Mass-Spectrometric Investigation ofthe Decomposition Products of Advanced Propellants and Explosives,"Space Sciences, Inc., August 1979 (AD-A074 963).

D-27 K. Kishore, "Comparative Studies on the Decomposition Behavior ofSecondary Explosives RDX and HMX," Defense Science Journal, Vol. 18,p. 59 (summarized in Chem. Abstr., Vol. 90, 206758), 1978.

D-2R A. E. Axworthy, J. E. Flanagan, and J. C. Gray, "Interaction of ReactionKinetics and Nitramine Combustion," Rocketdyne Division, Rockwell

International, Canoga Park, CA, Report AFATL-TR-80-58, May 1980 (AD-B052

861IL).

D-29 M. Boudart, "Kinetics of Chemical Processes," Prentice-Hall, New York,*Chapter 6, 1968.

I.5

)

/

U

1*

I

.

. , .APPENDIX A.

: REPORTED ARRHENIUS PARAMETERS FOR THERMAL DECOMPOSITION" OF HMX AND RDX IN THE VAPOR PHASE

6*"

So

.

K.

j"1

.'o.

I"

IB

APPENDIX A.

REPORTED ARRHENIUS PARAMETERS FOR THERMAL DECOMPOSITIONOF IIMX AND RDX IN THE VAPOR PHASE

Available valuesA- 1- 4 for gas-phase decomposition of HMX and RDX are

summarized in Table A-1, together with temperature ranges, kinetics, etc. Theactivation energy and frequency factor for gas phase decomposition of HMX havebeen determined by isothermal DSCA-I, 4 (see discussion accompanying AppendixB, p. 70-72), by very-low-pressure pyrolysisA- 2 and by a methodA- 3 involvingcombined manometric study of gas- and condensed-phase decomposition in. thevery early stages of the reaction. The DSC valuesA- I are much higher than

those determined by the other methods.A-2,A-3 Both DSC and VLPP data forHMXA- 1,2 show considerable scatter, but the VLPPA- 2 values seem more reliable

due to the larger temperature range (135* as compared to 120); thus, theactivation energy for gas-phase HMX decomposition iv the temperature range ca

250-400C would appear to be ca 33 kcal/mole, with a frequency factor of log A(sec -1 ) ca 12.8 although the authors point out that their data are too

scattered '-o completely rule out that 45.50 kcal/mole that would signifyinitial N-NO2 bond scission.A-i This value of ca 33 kcal/mole is in agreementwith the manometric values.A 3

The DSC valuesA- 1'4 for RDX decomposition in the vapor phase weremeasured over a wider temperature range (51° ) than for HMX (120), and the plotshows considerably less scatter; thus the RDX values measured by DSC seem muchmore reliable than the IIX values measured by DSC. For further discussion of

// DSC studies on vapor-phase HMX and RDX decomposition, see Appendix B.

Since HMX and RDX might be expected to decompose by similar mechanisms,it is interesting to note the general agreement between the manometricA 3 andVLPPA 2 values for HM and the values for RDX.A-1,3,4

A-R. N. Rogers and G. W. Daub, "Scanning Calorimetric Determination of Vapor-

Phase Kinetics Data," Anal. Chem., 11,p. 45, p. 596, 1973.

A-2 D. F. McMillen, J. R. 1Barker, K. E. Lewis, P. L. Trevor and D. M. Golden,

"Mechanisms of Nitramine Decomposition: Very Low-Pressure Pyrolysis of HMXand Dimethylnitramine," Final Report on SRI Project PYU 5787, Supported byDepartment of Energy through Lawrence Livermore Laboratories, Contract No.EY-76-C-03-0115, 18 June 1979.

A-3M. S. Belyayeva, G. K. Klimenko, L. T. Babaytseva, P. N. Stolyarov,

"Factors Determining the Thermal Stability of Cyclic Nitramines in theCrystalline State," Ffl-ID(RS)T-1209-78 (AD-B033 572L).

A-4R. M. Potter, G. J. Knutson, and M. F. Zimmer, Compat. Propellants Explos.

Pyrotechnics Plast. Addit., Conf. Pub. 1975, II-D., 12 pp., Chem. Abstr.,

Vol. 86, 142411j, 1974.

// 6

/

As discussed in the main body of the report, reactions on the containersurface probably are not influencing these values too much, although more work

r on this point would help since wall reactions do seem to influence dimethyl-nitramine decomposition.

Tables A-2 and A-3 show the actual data points reported by the authors ofReferences A-1-4 these were analyzed statistically as described in the mainreport (p. 19-26). Recommended values are given in the table in the mainreport, and the points are plotted in Figures 2 and 4 of the main report.

64

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67

APPENDI B.

/ REPORTED ARRHENIUS PARAMETERS FOR DECOMPOSITIONOF NEAT LIOU11D AND DISSOLVED HMX

69

APPENDIX B.

REPORTED ARRHENIUS PARAMETERS FOR DECOMPOSITIONOF NEAT LIQUID AND DISSOLVED HMX

Available valuesB--O for liquid-phase decomposition of HMX aresummarized in Table B-i, and solution-phase values in Table B-2, together with

temperature ranges, kinetics, etc.

The best literature set of Arrhenius parameters for thermal decompositionof neat liquid HMX (Table BI) seems to be che 52.7 kcal/mole and log A(sec -l)

of 19.7 reported by Robertson; this is based on the long temperature range

B-lA. J. B. Robertson, "The Thermal Decomposition of Explosives. Part II

Cyclotrimethylenetrinitramine and Cyclotetramethylenetetranitramine, "

Trans. Faraday Soc., Vol. 45, p. 85, 1949.

B-2R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energies with

a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p. 412, 1966.

B-3R. N. Rogers and L. C. Smith, "Estimation of Preexponential Factor from

Thermal Decomposition Curve of an Unweighed Sample," Anal. Chem., Vol 39,p. 1024, 196;.

B-4 E. K. Rideal and A. J. B. Robertson, "The Sensitiveness of Solid High

Explosives to Impact," Proc. Roy. Soc., Vol. 195A, p. 135, 1948.

B-5R. N. Rogers, "Differential Scanning Calorimetric Determination of Kinetic

Constants of Systems chat Melt with Decomposition," Thermochimia Acta,

Vol. 3, p. 437, 1972.

B-6 B. B. Goshgarian, "The Thermal Decomposition of Cyclotrimethylene-

trinitramine (RDX) and Cyclotetramethylenetetranitramine (HM')," AFRPL-TR-

78-76 (AD-B032 275L).

B-7D. A. Flanigan and B. B. Stokes, "HMX Deflagration and Flame

Characterization. Volume I. Phase II Nitramine Decomposition and

Deflagration Characterization," Thiokol Corporation, Huntsville Division,Huntsville, AL, Report AFRPL-TR-79-94, October 1980 (AD-B053 058L).

B-8R. J. Powers, "Hazards Due to Precomb~stion Behavior of High Energy

Propellants," AFATL, Private Communication, June 1980, of data presented at

JANNAF Workshop, Eglin AFB, April 1980.

B9yu. Ya. Maksimov, "Thermal Decomposition of Hexagen and Octogen," Tr. Mosk.Khim-Tekhnol, Inst. No 53, p. 73, 1967 see Chem. Abstr., Vol. 68,

p. 41742r. Translated bj H. J. Dahlby Los Alamos Report LA-TR-68-30, LosAlamos, 1968.

B-10 Maksimov (presumably), work summarized in K. K. Andreyev, "Thermal

Decomposition and Combustion of Explos.ves," FTD-HT-23-1329-68, p. 87,

p. 130 (AD-693 600).

71

/ . J/

covered (440); on the fact that the absence of any effect of sample size(varied from 1-7mg) suggests that self heating is not important; and on thelow degree of scatter in the Arrhenius plot. However some of the otherauthors do not state temperature range or provide enough information to enablethe degree of scatter to be evaluated. On reading Robertson's paper andexperimental reference cited therein, no obvious sources of systematic errorwere evident to this writer.

Most of the valuesB-i- 5 ,7 of A and Ea, measured at or below atmosphericpressure, given ii Table BI for decomposition of neat liquid HTD[ agree withina few kcal/mole with those of Robertson. The exceptions are the values ofReferences B-6 and B-8. However, these points were measured over the sbortesttemperature ranges in Table B-i and it is difficult to rule out thepossibility of self heating, since Reference B-6 states (p.10) that the samplesize was 2 mg, but it is stated on page 34 that "sample weight greater than1.0mg increased the isothermal t.inperature during HNX decomposition,apparently due to excess thermal evolution beyond the capabilities of theinstrument to adequately regulate a constant temperature."

Reference B-8 used sample sizes on the order of 1.5 mg, so self-heatingmay not be quite as bad. Robertson used sample sizes of 1-7 mg and found noe~f'ct of mass ie., apparently no self-heating. Possibly this is because inL"'Z 2-cm glass bulb or copper oven apparatus used by Robertson, the samplewould be more spr,,ad out than in a millimeter s .zed DSC pan.

Judging from the results in Table B-i, actilation energies and frequencyfactors seem to be independent of .'vpe and preesure of inert gases present upto 1 atmosphere; however, Judging from the data of 2eference B-7 it wouldappear that on going from 1 to 70 atmospheres, the acti-ation energy decreasesnoticeably, from ca 56 kcal/mole at 1 to ca 42 kcal at 70 atmospheres. Theseresults are least squares averages and appLir independent of particle si:'e.

In addition to the data given in Tables B-I and B-2, R. N. RogersB-llfurnished several points for decomposition of neat liquid HM, measured byisothermal DSC with corcection for the concurrent gas-phase reaction.powersB-8 on the other hand, in his studies of the decomposition of neatliquid HMX by isothermal DSC, felt that the gas-phase decomposition wassufficiently unimportant to be neglect.d; this is in agreement withGoshgarian'sB-6 observation that the decay portion of HNKX decomposition curvesappeared smooth throughout the decomposition, However for spread -ample agas-phase "hump" could be seen. Thus the gas-phase dczomposition seems lessimportant for HMX than for RDX. In any case, Powers' data were obtained inthe initial phase of the liquid decomposition, where the vapor phase should beproportionately least important; thus they wire included along withRobertsonsBI and Rogers' gas-phase-corrected data, in the best three sets ofdata on liquid-phase HMX decomposition.

The actual data points obtained by Robertson,B-1 RogersB-f1 and PowersB-8

are given in Table B-3. These points were analyzed statistically as given in

B-1R. N. Rogers, Los Aiamos Scientific Laboratories, Private Communication,

February 1980.

72

the main report, and plotted in Figure 3 of the main report. Note, however,that while the picture of concurrent liquid and vapor-phase reactions beingthe main contributors to the shape of - DSC curves stll seems to hold for

RDX, it has recently begun to appearl -O ,1l that the situation for HX may bemore complicated, possibly as a result of complications due to presence of thnon-volatile residue. Until this situation is understood better than it is apresent, it may well be a good idea to just use Robertson's manometric data athe best data for decomposition of liquid ,HMX. As shown in Table B-3, thisgives E. a 53.1 kcal/mole and log A (sec ) - 19.950.

There are only a few values for decomposition of HMX in solution. Thevalue of 50.3 kcal/mole in Convalex-lO was measured by dynamic DSC, and thereis no information on the temperature range covered. The data ofMaksimovi-9 , were done over a fairly large j56-C) temperature range, and thdegree of scatter in the Arrhenius plot given, does not seem unreasonable.Thus it does not seem unreasonable to conclude from thc data in Tables B-2 anB-1, that the activation energy and frequency factor for decomposition of HMin an inert solvent are somewhat lower than those for neat liquid HHX,although the data for HHX in solution were not reanalyzed statistically by thpresent writer.

-- 3

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-47

APPENDIX C.

REPORTFD ARRHENIUS PARAMETER~S FOR DECOMPOSITIONOF NEAT LrOUTD AND DISSOLVED RDX

79

APPENDIX C.

-. .7 REPORTED AR.HENIUS PARAMETERS FOR DECOMPOSITION- - OF N..AT LIQUID AND DISSOLVED RDX

Available kinetic parametersC- 1- 3 1 for decomposition of RDX in the neatliquid phase and in solution are summarized in Tables C-I and C-2, respectively.

C-IA. J. B. Robertson, "The Thermal Decompositon of Explosives. Part II.

Cyclotrimethylenetrinitramine and Cyclotetramethylenetetranitramine,Trans. Faraday Soc., Vol. 45, p. 85, 1949.

C-2A. J. B. Robertson, S.A.C. No. 4885, referred to in Reference 5.

C-3G. K. Adams, S.A.C. No. 5766, "The Thermal Decomposition of RDX," February

1944.

C-4A. J. B. Robertson, S.A.C. No. 3264, referred to in Reference 5.

C-5j. Wilby, "Thermal Decomposition of RDX/TNT Mixtures, Part I," A.R.D.E.

Report (MX) 16/59, AD-225 991, August 1959.

C-6C. E. H. Bawn, J. K. Hays and F. H. Pollard, "The Thermal Decomposition ofTetryl and RDX," S.A.C. No. 2025, April 1942.

C-7A. J. B. Robertson and R. P. Sinclair, "The Thermal Sensitivity of

Explosives," S.A.C. No. 1596, January 1942.

SC- 8 F. C. Rauch and R. B. Wainwright, "Studies on Composition B, " Final

Report, Contract No. DAAA21-68-C-0334, American Cyanamid Company, February1969, AD-850-928.

"C'F. C. Rauch and A. J. Fanelli, "The Thermal Decomposition Kinetics ofHexahydro-1,3,5-trinitro-s-triazene above the Melting Point: Evidence forboth a Gas and Liquid-Phase Decomposition,", J. Phys. Chem., Vol. 73,p. 1604, 1969.

ClOF. C. Rauch and W. P. Colman, "Studies on Composition B," Final Report,

Contract No. DAMA 21-68-C-0334, American Cyanamid Company, March 1970, AD-869 226.

1C-flR. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energies

with a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p. 412,1966.

" OC-2R. N. Rogers and L. C. Smith, "Estimation of Preexpo-ential Factor from

• Thermal Decomposition Curve of an Unweighed Sample," Anal. Chem., Vol. 39,* pp. 1024-5.

mo . 81

3I'

C-13R. N. Rogers and G. W. Daub, "Scanning Calorimetric Determination of

Vapor-Phase Kinetics Data," Anal. Chem., Vol. 45, p. 596, 1973.

C- 14R. N. Rogers, "Determination of Condensed-Phase Kinetics Constants,"

Therochimica Acta, Vol. 9, p. 444, 1974.

.C-15p G. Hall, "Thermal Decomposition and Phase Transitions in Solid

Nitramines," J. Chem. Soc., Faraday Trans., Part II. Vol. 67, p. 556,1971.

C- 16K. Kishore, "Thermal Decomposition Studies on Hexahydro-1,3,5-trinitro-s-triazene (RDX) by Differential Scanning Calorimetry," Propellants andExplosives, Vol. 2, p. 78, 1978.

C- 17T. B. Joyner,"Thermal Decomposition of Explosives. Part I. Effect of

u Asphalt on the Decomposition of Asphalt-Bearing Explosives," NWC TP 4709,I March 1969, AD-500 573.

C-18J. Harris, "Autoignition Temperatures of Military High Explosives by

Differential Thermal Analysis," Thermochimica Acta, Vol. 14, p. 183, 1976.

'" C-l9J. Harris and E. Demberg, "AutoignLtion Temperatures of Military High

Explosives by Differential Thermal Analysis," PATI 4481, March 1973, AD-908 846L.

* 0-20T. G. Floyd, "Reaction Kinetics of Temperature-Cycled Cyclotrimethylene-

trinitramine (RDX)," Journal of Hazardous Materials, Vol. 2, p. 163,1977/78.

C-21W. P. Colman and F. C. Rauch, "Studies on Composition B," Final Report,

Contract No. DAAA21-70-0531, American Cyanimid Company, February 1971.,AD-881 190.

i C-22J. Wilby, "Thermal Decomposition of RDX/TNT Mixtures, Part I.," A.R.D.E.

I- Report (MX) 16/59, August 1959, AD-225 991.

.C-2 3 . Wilby, "Thermal Stability of RDX and HMX Compositions, Particularly

their Mixtures with TNT," Symp. Chem. Probl. Connected Stab. Explos.,(Proc.), pp. 51-65, 1967, for availability see Reference C-24, 1968.

C-24D. F. Debenham and A, J. Owen, "The Thermal Decomposition of 1,3,5-

* trinitro-hexahydro-1,3,5-triazine (RDX) in 1,3,5-Trinitrobenzene," Symp.Chem. Probl. Connected Stab. Explos., (Proc.) 1976' Vol. 4, pp. 210-20;1977, can be ordered from the Secretary, Tekn Lic Stig Johansson,Sektionen for Detonik och Forbranning, Box 608, S-551 02 Jonkoping,

*Sweden. Postal Account No. 507690-6, Banking Account Gotabanken No. 652-* 4383.

Y25yu. Ya. aksimov, "Thermal Decomposition of Hexogen and Octogen," Tr.

Mosk. Khim.-Tekhnol, Inst. No. 53, p. 73, 1967, see Chem. Abstr., Vol. 68,p. 41742r., Translated by H. J. Dahlby, Los Alamos Scientific LaboratoryReport LA-TR-68-30, Los Alamos, NM, 1968.

82

I%N

C-26Maksimov (Presumably), work summarized in K. K. Andreyev, "Thermal

Decomposition and Combustion of Explotives," FTD-HT-23-1329-68, p. 87,p. 130 (AD-693 600).

C-27K. K. Miles, "The Thermal Decomposition of RDX," Master's Thesis, Naval

Postgraduate School, Monterey, March 1972 (AD-743 762).

C-28D. A. Flanigan' and B. B. Stokes, "HMX Deflagration and Flame

Characterization," Volume I. Phase II Nitramine Decomposition andDeflagration Characterization," Thiokol Corporation, Huntsville Division,Huntsville, AL, Report AFRPL-TR-79-94, October 1980 (AD-B053 058L).

C-29R. M. Potter, G. J. Knutson, and M. F. Zimmer, "Effect of Dibutyl Tin

Dilaurate nn the Thermal Decomposition of RDX," Compat. Propellants,Explos. Pyrotechnics Plast. Addit., Conf. 1974, 11-0, 1975.

C-30K. Kishore, "Comparative Studies on the Decomposition Behavior of

Secondary Explosivea RDX and HMX," Defense Science Journal, Vol. 18,p. 59, 1978, summarized in Chem. Abstr., Vol. 90, 206758v.

C-31p. W. M. Jacobs and A. R. T. Kureishy, J. Chem. Soc., p. 4718, 1964.

83

Due to the long temperature range, low degree of scatter in the Arrheniusplots, and care to avoid such sources of error as self heating, the best pairof Arrhenius parameterl for the decomposition of liquid RDX is probably thatgiven by RobertgonC-l, (Table C-1).

However, there remains the problem of Xaporization followed by gas-pha~ereactions. Robertson's other set of datac- are probably in error as Wilby

V 5

quotes Reference C-4 as saying that the values may be in error due to poorequilibliyv and to gas-phase decompositipn, The values of Bawn, gas andPollard t and of Robertson and Sinclair " are probably in error - due toshort temperature range 8ni Jarge sample sizes leading oo3 self heating. Alongwith Robertson's values, -

' the values of G. K. Adams were accepted byWilby - as the best values. However, examination of Table I of Adams'reportc- 3 reveals that while the values for the experimentally determinedlog10k and the calculated log k lc match each other they did not matchva exp " from the state Arrhenius parameters, and the plot of thevalues calculatedurmth t

values given for log k shows a large degree of scatter. The source of10 calcthis discrepancy is unknown to the present writer. Until it is explained itwould probably be best to disregard the data given in Reference C-3.

The group at American CyanamidC- 8,9,10 decomposed RDX in reactors of

constant known volumes and followed the reaction by gas chromotographicanalysis of the undecomposed RDX. This has an advantage over manometricdetermination, since it is not subject to errors due to secondary reactionsamong gaseous products, although the manipulations necessary to quench thereaction in each reactor individually appear to have limited the temperaturerange to 20. The rate constants were independent of inizial mass, reactorvolume or added pressure of NO2 or helium.

The results described in this series of reporhs illustrate the importanceof statistical analysis. The preliminary values (log A-19.2, Ea-48.7 )were obtained from a preliminary analysis, but a subsequent least squaresanalysisC - 10 yielded log A - 22.4 and Ea - 55.6 kcal/mole. The differenceseems large enough to be chemically significant. This illustrates theimportance of applying statistical analysis when estimating Arrheniusparameters from kinetic data, since it is evidently difficult to "eyeball" a

slope and intercept with sufficient accuracy.

JoynerC - 17 carried out manometric studies on the decomposition of RDX;the data were believed satisfactory despite some problems with sublimation andpressure fluctuation. In agreement with this the three points, plotted forneat liquid RDX appear to fall on the same line (main report, Figure 1) and

the rate constants seem to agree reasonably well with those of Robertson' -''2

and of the American Cyanamid grout.C-l0

Thermal analysis studies will be considered in two parts - first theisothermal DSC and DTA, then dynamic or temperature-programmed studies. Webegin wt 4 isothermal DSC results. The best isothermal DSC result is that ofRogers, who obtained log A (sec- ) 18.3 and Ea = 47.1 kcal/mole fromexperiments in which correction was made for gas-phase reaction which proceedsconcurrently with the liquid reaction. To this writer's knowledge, this isthe only study in which a quantitative correction for vapor-Rhase reaction hasbeen Varried out. Comparison with the uncorrected valuesC- 13,14 of log A(sec - ) - 16.4 and Ea - 43.1 kcal/mole reveals that the correction is of the

84

7'

order of a factor of 100 in A and a difference of 4 kcal/mole in ac*'.. Lionenergy for DSC measurements of heat output using the Perkin-Elmp-- o.3-IBapparatus of Reference C-14; but the magnitude of the correr-'_,, will ofcourse vary with the mass/volume ratio and the geometry of the system. Sincethe other isothermal DSC studiesC 16,20,28-30 made no attempt to correct theirresults specifically for the gas-phase reaction it is not surprising to notethat their activation energies and frequency factors fall somewhat lower thanthe best DSC C- 14 and kineticC- 1 '2 '8 -1 0' 17 values.

In addition to the above error (previous paragraph) due to vapor-phasereaction, non-isothermal thermal analysis experiments would be affected by avariation with temperature of the proportion of the vapor-phase reaction; thisis in addition to any errors introduced in the derivation of the Kissingerequation (see p. 17-19) or other method used to estimate kinetic parameters.None of these studies attempts to correct for gas-phase reaction.Consequently, while all non-isothermal thermal analysis stud'es of which thiswriter is aware have been tabulated they will not be discus! ' individually.

Activation energies for decomposition of RDX in solution (Table C-2) seemto be generally several kcal/mole lower than the values (Table Cl) for theneat liquid. RobertsonC- I found values for log A (sec-1 ) and activationenergy (ca 15.5 and 41 kcal/mole respectively) that were noticeably lower thanhis values (18.5 and 47.5) for the neat liquid. However, the values in TNTmay be affected by concomitant decomposition of TNT; see following paragraph.

The work of WilbyC- 2 2'2 3 was done over a short (17-180) temperaturerange, using large samples which might have led to self-heating; furthermore,Wilby pointed out that TNT was decomposing at the same time as RDX and thatthis might have complicated matters. However, the Arrhenius parameters werein reasonable agreement with those of Robertson.C -1 This agreement for suchlarge sample size may suggest that self heating is not a source of error fordecomposing RDX in TNT and possibly in inert solvents generally; however, notethe short temperature range in Wilby's measurements. The Russian workers alsofoundc- 25 ,26 that log A (sec- 1) and E. were lower in solution indinitrobenzene than were the best values for liquid RDX.

The value of '7.13 obtained by JoynerC- 17 is somewhat higher than thevalue of about 14-.6 obtained in the other entries of Table C-2. However,this is to be expected since it was obtained by assuming an activation energy(44.2 kcal/mole) determined for neat liquid RDX; this value is higher thanmost of those in Table C-2 and would thus be expected to lead to a higherfrequency factor.

The above studies were all done manometrically. Colman and Rauch0- 2 1

studied the decomposition in TNT kinetically, by analysis of undecomposed RDX;this would reduce errors due to vaporization followed by decomposition of RDXin the vapor phase. This is especially pertinent since while RDXdecomposition seems unaffected by TNT, the TNT decomposition is accelerated inthe presence of more than a 5% concentration of decomposing RDX; thecomposition of the gaseous products appears to be a superposition of thosefrom RDX and TNT alone. Thus, while Robertson's values for 1% and 5% RDX inTNT are probably not in error from this source, studies using more than about5-10% RDX and TNT may be in error. However, the errors in Ea and Log A may

85

\\A

\ _______

not be too great since it was foundC- 2 1 that activation energies fordecomposition of RDX and of solvent were about the same within the ratherlarge (± 5 kcal/mole) error limits.

Debenham and OwenC-24 also followed the reaction by analysis ofundecomposed RDX. Considering the short (100) temperature range, theirapproxinate activation energy of 46 kcalimole seems essentially the same asthe other values in Table C-2 although a bit on the high end of the range.

Rogers and MorrisC -l f obtained an activation energy of 48.4 kcal/mole byDSC, in Convalex-10 (polyphenyl ether). This value is about the same as thebest values in Table C-2 for the decomposition of neat liquid RDX, butsignificantly lower than the value (67.4 kcal/mole) reported on the sameapparatus by Rogers and MorrisC-ll for decomposition of liquid RDX; thus, the

activation energy for RDX in solution is still less than for the neat liquid,when the two are determined by the same method on the same apparatus.

Table C-3 lists the rate constant and temperature data usedC- 1,10,14,17

in what, on the basis of the above discussion, the present writer feels to be

the most reliable studies on decomposition of liquid RDX. These data wereanalyzed together on a common axis (main report, Figure I, Table and

accompanying discussion) to give the best values for log A (sec-1 ) and Eareported there. Table C-3 also gives the values obtained when rhe programsused in the present report were applied to the data from the it. ividual datasets; values reported by the individual authors are given in Taole C-I.

Table C-4 lists the actual rat2 constant and temperaturedata,C - L,17 ,2 1,22 used in what the present writer feels, on the basis of the

above discussion, to be the most reliable data for decomposition of RDX insolution in TNT. These data were plotted together on a common axis (mainreport, Figure 5) and the data were analyzed statistically as described in themain report (Table and accompanying discussion) to give the suggested valuesfor log A (sec-1 ) and Fa reported there. Table C-3 also gives the valuesobtained whea the programs used in the present report were applied to the datafrom the individual data sets; values reported by the individual authors aregiven in Table C-2.

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APPENDIX D.

REPORTED ARRHENIUS PARAMETERS FOR THERMAL DECOMPOSITIONS OFIM AND RDX AT TEMPERATURES B~ELOW THEIR MELTING POINTS.

95

'°

APPE."

REPORTED ARRHENIUS PARAMETERS FOR THERMAL DECOMPOSITIONS OFHMX AND RDX AT TEMPERA' 'RES BELOW THEIR MELTING POINTS.

Available values - -2 7 for decomposition of HMX and RDX at temperaturesbelow their melting points are summarized in Tables D-1 and D-2.

U'.

.

D-IB. B. Goshgarian, "The Thermal Decomposition of Cyclotrimethylene-

trinitramine (RDX), and Cyclotetramethylenetetrr..tramine (HMX)," AFRPL-TR-78-76, October 1978 (AD-B032 275L).

D-2Yu. Ya. Maksimov, "Thermal Dec.- 4cion of Hexogen and Octogan," Tr. Mosk.

Khim. Tekhnol, Inst. No. 53, p. 73, see Chem. Abstr., Vol. 68, p. 41742r,Translated by H. J. Dahlby, Los Alamos Report LA-TR-68-30, Los Alamos, NM,1968.

D-3Haksimov, work summarized in K. K. Andreyev, "Thermal Decomposition andCombustion of Explosives," FTD-HT-23-1329-68, p. 87, 130 (ADI-93 600).

D-4G. K. -as "Chemistry of the Solid State," personal communir .iton

referred to by C. H. Bawn, W. H. Garner, ed., Butterworths, Lon%;,mn, p. 265,

1 1955.DD-5

" -G. K. Adams, "The Thermal Decomposition of RDX," S. A. C. 5766, 1 February

1944.

.D6C. E. H. Bawn, "Chemistry of the Solid State," W. E. Garner, ed.,

I Butterworths, London, p. 261, 1955.

J. J. Batten and D. C. Hurdie, "The Thermal Decomposition of RJ)X at

r Temperatures Below the Melting Point. II. Activation Energy," Aust. J.Chem., Vol. 23, p. 749, 1970,

•-j. J. Batten "The Thermal Decomposition of RDX at Temperatures Below theMelting Point. IV. Catalysis of the Decomposition by Formaldehyde," Aust.

J. Chem., Vol. 24, pp. 2025-9, 1971.

"-9 K. K. Miles, "The Thermal Decomposition of RDX," Master's Thesis, U.S.Naval Postgraduate School, Monterey, CA, March 1972 (AD-743762).

.D-lp. G. Hall, "Thermal Decomposition and Phase Transitions in Solid

Nitramines," J. Chem. Soc., Faraday Trans. Part 2, Vol. 67, p. 556, 1971.

" D'II E. Medvedev, G. V. Sakovich, and V. V. Konstantinov, "NonisothermalKinetics of the Solid-phase Decomposition of Octogen," Tezisy Dokl.Sovesch. Kinet. Mekh. Khim. Reakts. Tverd. Tele., 7th., Vol. 1, pp. 163-5,1977, Chem. Abstr., Vol. 88, p. 177810g, 1978.

97

LN

" D-12R. R. Miller, R. C. Musso, and A. F. Grigor, *Combustion Mechanisms of Low

Burning Rate Propellant," AFRPL-TR-69-130, May 1969 (AI)-502957).

D-13 S.(sic) Goshgarian, private communication cited in K. P. McCarty, HMXPropellant Combustion Studies," AFRPL-TR-76-59 (AD-BO17 527L).

D-14 W. Hoondee, "The Thermal Decomposition of 0-HMX ," Master's Thesis, NavalPostgraduate School, Monterey, CA, June 1971 (AD-728 582).

D-15j. E. Sinclair and W. Hoondee, "The Thermal Dccomposition of 0-HMX ,

Proc. Symp. Explos. Pyrotechnics, 7th, 1-5, 1-4, (Chem. Abstr., Vol. 76,

143050w), 1971.

* D-16J. N. Maycock and V. R. Pai Vernecke- , "Thermal Decomposition of 0-HMX

(Cyclotetramethylene Tetranitramir j," Explosivestoffe, Vol. 17, p. 5,

0 1969.6 tr

' :, - -ana and R .. Graybush, "Thermal Decomposition cf 1,3,5,7-Tetranitro-,.r -;-raazacyclooctane (HMX): A Mass Spectrometric Studyof the Products from 0-HMX ," Ind. Chim. Belg., Vol. 32, Spec. No. Part 3,

pp. 647-50, "j7.D-1

-18 B. Suryanarayana, V. I. Siele, and J. Harris, unpublished work cited in

Reference 19.

D-19B. Suryanarayana, J. R. Autera, and R. J. Graybush, "Mechanism of Thermal

Decomposition of HMX (1,3,5,7-Tetranitro-1,3,5,7-Tetraazacyclooctane),"Proceedings of the 1968 Army Science Conference, (OCRD) West Point,Vol. 2, p. 423, .968 (AD-837 173).

D-20j. E. Sinclair and W. Hoondee, "Thermal Decomposition of t -HMX,"

Jahrestag, Inst. Chem. Treib., Explosivestoffe Fraunhofer-Ges. 1971, Pub.

1972, 57, Chem. Abstr., Vol.81, 108070j.

I D-21R. N. Rogers and E. D. Morris, Jr., "On Estimating Activation Energieswith a Differential Scanning Calorimeter," Anal. Chem., Vol. 38, p. 412,

1966.

* D-2 2M. S. Belyayeva, G. K. Klimenko, L. T. Babaytseva and, P. N. Stolyarov,

I"Factors Determining the Thermal Stability of Cyclic Nitroamines in the

Crystalline State," FTD-ID (RS) T-1209-78, AD-B033 572L.

D-23J. Kimura and N. Kubota, "Thermal Decomposition Process of HMX,"

- Propellants and Explosives, Vol. 5, p. 1, 1980.

D-24 K. Takaira and K. Okazaki, M.S. Thesis, National Defense Academy, 1974,

cited in Reference 23, 1974.

D-2 5B. Gosharian, Private Communication, August 1976, cited in Reference 23.

D 2 6 M. Farber and R. D. Srivastava, "A Mass-Spectrometric Investigation of theDecomposition Products of Advanced Propellants and Explosives," SpaceSciences, Inc., August 1979 (AD-A074-963).

98

S

D-2 7K* Kishore,."Comparative Studies on the Decomposition Behavior of

Seconrtry Explosives RDX and HMK," Defense Science JournaL, Vol. 18,

p. 59, (summarized in Chem. Abstr., Vol. 90, 206758), 1978.

99

As discussed elsewhere (Section IV. D. of the main report), decompositionof HMX and RDX at temperatures below their melting points is most likely acomplex process involving the liquid and vapor states as well as the solidstate. Furthermore, the activation energies and frequency factors appear tobe dependent on factors like degree of spreading of the sample (see forexample Reference D-7) which are often difficult to evaluate in view of thelimited information given in many of the reports. Therefore, although anattempt has been made to include all available values in Tables D-I and D-2,we will confine ourselves to pointing out some of the main trends in the data.

One trend is a tendency for activation energies measured at or near themelting point by TGAD- 2 5 , DSCD- 9,1 0, 2 1 ,2 3 ,24 or FRHSD -l techniques to havewhat seem to be unreasonably high values, sometimes well over 200 kcal/mole.Possibily these values are artifacts resulting from complexity in the behaviorof the material as it simultaneously melts and decomposes (see p. 35 of themain report).

knother pattern is that manyD - I1'14 '1 5 '17 20 '2 5 (but not all) of thestudies on HMX decomposition show changes in activation energy in the regionaround approximately 245 ± 150C. The magnitude and exact locations of thesechanges are not reproducible from study to study, except that they generally

fall in the approximate range 230-60°C.

An attempt D- 28 at applying autocatalytic solid reaction kinetics to HMXdecomposition yielded an activation energy of 140 kcal/mole and a frequencyfactor of 4.76 x 1035 . However, the significance of these numbers seemsuncertain; for one thing, the kR in equation 6.4.2 of Reference D-29, which isequated by the authors of Reference D-28 to a rate constant, is described in

Reference D-29 as an "adjustable parameter;" the justification for relating itto a rate constant is not obvious. Also, according to this treatment tle rateconstant comes out with units of time raised to the power of -3.5, althoughrate constants generally, because of the manner of their derivation, areexpected to be expressed in terms of $reciprocal (time multiplied by(concentrationn-l). If the term k t in equation 6.4.2 of Reference D-29 is

replaced by (kt), and k (- (k ) is considered as a rate constant havingdimensions sec- ', It would yield values of log A and Ea that would be lowerby a factor of 8 (-3.5, Reference D-28) than those (log 1 o A - 35 and Ea - 143

kcal/mole) given in Reference D-28, or logl0 A(sec- 1) 10 and Ea 40kcal/mole.

Belyaeva et al. D - 22 have reported a series of manometric studies on HMXand RDX decomposition in which separate account was taken of the gas and

D-28 A. E. Axworthy, J. E. Flanagan, and J. C. Gray, "Interaction of Reaction

Kinetics and Nitramine Combustion," Rocketdyne Division, RockwellInternational, Canoga Park, CA, Report AFATL-TR-80-58, May 1980 (AD-B052861 L).

>-29 M. Boudart, "Kinetics of Chemical Processes," Prentice-Hall, New York,

Chapter 6, 1968.

100

condensed phase decompositions; the gas- and condensed-phase rates were

evaluated separately from the following equation:

__ ~dn . V 2 +s L-.

where A - 273/76OV. T, B - 273R/760M; K1 and K2 are the decomposition rates inthe gas and condensed phases respectively; V is the volume of products up to agiven point in time; V is the final volume of conversion products; m0 is thesample weight, and H is molecular weight; and dn/dt is the total rate ofthermal decomposition.

Initial rate data in the gas-'and condensed phases are given in AppendixA and in the final lines of Tables D-1 and D-2 respectively. The condensed-phase Arrhenius parameters in Tables D-1 and D-2 are based on statisticalanalyses done by the present writer; the original Russian authors of ReferenceD-22 did not report Arrhenius parameters from their condensed phase data; itshould be noted that this may well be the result of well-founded doubts as totheir exact significance. Nevertheless, it seemed worthwhile to carry out thestatistical analyses whose results are summarized in the last two lines ofTables ]>-I and D-2. The "condensed phase" Arrhenius parameters or temperaturecoefficients of reaction are significantly lower for tHX than for RDX; in factthe frequency factor for H(X (log A(sec- 1) - 9.1, Table D-2) is in a rangethat in the gas phasT would be characteristic of a bimolecular reaction, whilethat for (log A(sec-) - 13.5) is In a region that in the gas phase would bemore characteristic of a unimolecular reaction. Possible reasons for thisdiscrepancy include (a) differences in chemical mechanisms for the solid-statedecomposition of 1MX and RDX; and (b) differences in kind or contribution ofphysical mechanisms, in particular vaporization and gas-phase decomposition ofHX and RDX, and liquefaction of the solid phase due to condensation ofproducts such as hydroxymethylformamide.

101

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APPENDIX E.

COMPUTER PROGRAM USED FOR LEAST-SQUARES FIT OF ORIGINAL

DATA

JI

APPENDIX !n.

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112

APPENDIX F.

COMPUTER PROGRAM USED FOR LEAST SQUARES FIT OF LOGARITHMS

OF DATA

113

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Edwards AFB, CA 93523 ATTN: M.K. King5390 Cherokee Avenue

1"AFWL/SUL Alexandria, VA 22314

Kirtland AFB, 114 871171."NASA

• .ORLangley Research CenterfATTN: L.ATTN: G.B. Northam/MS 168

OATTN: L.H. Caveny Hampton, VA 23365Bolling Air Force BaseWashington, DC 20332

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ATTN: 1. Huggins ATTN: R.R. MillerD.G. Vutetakis P.O. BOX 210

505 King Avenue Cumberland, MD 21501Columbus, OH 43201

Hercules, Inc.

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ATTN: A. Dean ATTN: K.P. McCarty

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P.O. Box 8 Magna, UT 84044Linden, NJ 07036

" Hercules, Inc." Ford Aerospace and Bacchus Works

Communications Corp. ATTN: K.B. Isom

DIVAD Division P.O. Box 98niv. Hq., Irvine Magna, UT 84044ATTN: D. Williams

' Main Street & Ford Road 1 Hercules, Inc.4_ Newport Beach, CA 92663 AFATL/DLOL

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MS MN50-2000General Electric Company 600 2nd Street NE2352 Jade Lane 55343Schenectady, NY 12301 Hopkins, MN

G E i aHoneywell, Inc.-General Electric Ordnance Senior Development Engineer

Systems ATTN: J. KennedyATTN: J. Mandzy 5901 South County Road 18

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I IBM Corporation. I General Motors Corp. ATTN:. A.C. Tam

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I Hercules, Inc. I lIT Research Institute

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ATTN: H.S. Pergament 1 University of California

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I United Technologies 2 United Technologies Corp.

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Huntsville Division

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1

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