Summary

The determination of impact sensitivity of high explosives (HE) isthe most commonly used way of evaluating an explosive hazard.Because of the diversity of practical conditions that make an explosionpossible, many experimental methods for measuring sensitivity havebeen developed. Therefore, the prediction of sensitivity to impact ofenergetic materials is essential.

This work discusses a criterion that aids in such screening for allfamilies of energetic substances. This criterion is based on the max-imum heat of reaction. The results of our research reveal a satisfactorymutual interfamily relation between both the theoretical criterion ofsensitivity (CS) and experimental values.

1. Introduction

All previous works about impact sensitivity of explosives

have revealed the existence of several series of correlations

between this property and different physicochemical para-

meters such as the oxygen balance(1±4), the molecular

electronegativity(5), the dissymmetry of charges around the

speci®c linkage to the fundamental state and to the excited

state(6), the heat of explosion(7). These different relation-

ships have been studied according to the nature of the

explosophore linkage, that is to say, by separating the dif-

ferent families of explosives (nitramines, nitroaromatics,

nitric esters . . .).

Another study has been led by H. Nefati(8). Contrary to

methods described previously, this statistical and neural

study regroups the different chemical explosives families.

Nevertheless, the quantity of parameters implemented in

this predictive model doesn't allow the reasons for this

sensitivity to be explained.

2. Prediction of Impact Sensitivity

2.1 Object of the Calculation

In fact, there is no correct interfamily theory to connect

impact sensitivity to the chemical structures of the com-

pounds studied.

In this work, we have ®rstly used the C4 criterion pro-

vided by the CHETAH code(9) to classify some explosives

according to their decomposition mode on impact.

Further to this study, as the CHETAH database allows

neither the drawing of all explosives such that NTO nor the

calculation of the C4 criterion for mixtures, we have de®ned

a reaction model applicable to the sensitivity criterion CS

so as to predict impact sensitivity not only for energetic

molecules but also for carbon, hydrogen, oxygen and

nitrogen explosive formulations.

2.3 CHETAH: Application to Impact Sensitivity

Application

CHETAH is software, developed by the American

Society for Testing and Materials (A.S.T.M)(9,10) which

allows the thermal stability, the energy hazard potential and

Prediction of Explosives Impact Sensitivity

Maryse Vaullerin and Andre Espagnacq

GIAT Industries, Centre de Bourges, 7 route de Guerry, F-18023 Bourges Cedex (France)

Luc Morin-Allory

Institut de Chimie Organique et Analytique, URA CNRS 499, Universite d'OrleÂans, F-45067 OrleÂans Cedex 2 (France)

Voraussage der Schlagemp®ndlichkeit von ExplosivstoffenDie Bestimmung der Schlagemp®ndlichkeit von Hochleistungs-

sprengstoffen (HE) ist die am meisten angewandte Methode zurBewertung einer GefaÈhrdung durch Sprengstoffe. Aufgrund unter-schiedlicher Voraussetzungen in der Praxis fuÈr eine moÈgliche Explo-sion, wurden viele experimentelle Methoden zur Messung derEmp®ndlichkeit entwickelt. Daher ist eine Voraussage der Schlag-emp®ndlichkeit energetischer Materialien wichtig. Die vorliegendeArbeit diskutiert ein Kriterium als Hilfsmittel zur Ausleuchtung allerenergetischen Substanzfamilien. Dieses Kriterium basiert auf dermaximalen ReaktionswaÈrme. Die Ergebnisse unserer Untersuchungenzeigen eine zufriedenstellende gegenseitige interfamiliaÈre Beziehungzwischen dem theoretischen Kriterium der SensibilitaÈt (CS) und denexperimentellen Werten.

PreÂdiction de la sensibilite aÁ l'impact des explosifsLa deÂtermination de sensibilite aÁ l'impact des explosifs est une des

voies les plus communeÂment employeÂes pour eÂvaluer le risque pyro-technique. A cause de la diversite des conditions expeÂrimentalesconduisant aÁ une reÂaction, beaucoup de meÂthodes expeÂrimentales pourla mesure de la sensibilite aÁ l'impact ont eÂte deÂveloppeÂes. Donc lapreÂdiction de cette sensibilite aÁ l'impact des mateÂriaux eÂnergeÂtiques estessentielle.

Ce travail preÂsente le criteÁre de sensibilite CS pour effectuer un teldeÂcriptage pour toutes les familles d'explosifs reÂunies. Il se base sur lapreÂdiction aÁ partir de l'enthalpie maximale de reÂaction. Les reÂsultats denotre recherche reÂveÁlent une correÂlation interfamilles satisfaisanteentre ce criteÁre de sensibilite CS et les valeurs expeÂrimentales.

# WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998 0721-3115/98/0306±0155 $17.50�:50=0

Propellants, Explosives, Pyrotechnics 23, 237±239 (1998) 237

the maximum heat of reaction of a compound to be esti-

mated.

R. D. Coffee(10) referred to the Benson theory of groups(11)

to create the thermochemical calculation code, CHETAH.

This code deduces from four criteria including the C4

criterion to thermodynamic data for compounds and pro-

ducts of reaction.

C4 Criterion

This criterion is represented by the empirical equation:

C4 � 10DH2max �Mn

DHmax: Maximum reaction heat (kcalyg)

M: molecular weight (g)

n: number of atomsygram

2.3 Criterion of Sensitivity for Molecules and Explosive

Formulations

The prediction of impact sensitivity of molecules and

explosive formulations is based on the criterion CS for

Criterion of Sensitivity which is the same as that of C4

because the parameters are de®ned in relation to the gross

formula CaHbNcOd and to the reaction equation as follows:

CaHbNcOdÿÿÿÿÿÿÿ!DHmax c

2N2 � b

2H2O

� d

2ÿ b

4

� �CO2 � aÿ d

2� b

4

� �C

CS � 10DH2max �Mn

DHmax: Maximum reaction heat (kcalyg)

M: molecular weight (g)

n: number of atomsygram

3. Results and Interpretation

Table 1 and Figure 1 show the results of the sensitivity

criterion CS as a function of the impact sensitivity coef®-

cient (ISI) whose experimental values are given in Refer-

ences 11±14.

In the case of impact sensitivity for classical organic

explosives, the criterion CS varies between 70 kcal2ymol

and 320 kcal2ymol.

With reference to Figure 1, we can see not only three

areas of sensitivity (high, medium, low) but also, con-

sidering the diversity of experimental data, the existence of

a thermochemical criterion CS for interfamily classi®cation

of explosives.

Table 1. Interfamily Explosive Classification

Acronym Chemical Name Ref. Impact SensitivitySensitivity Criterion

CSI CSN m kcal2 molÿ1

NGl Nitroglycerin 11 0.2 289.1EGDN Nitroglycol 11 0.2 284.3Sorguyl 1,3,4,4-Tetranitroglycoluril 11 1.5±2 295.9PETN Pentaerythritol tetranitrate 11 3.0 251.1Tetryl Tetryl 11 3.0 232.5NC (14.14% N) Nitrocellulose 11 3.0 199.4HNS Hexanitrostilbene 11 5.0 218.6TetNA 2,3,4,6-Tetranitroaniline 11 6.0 242.1TNPy Trinitropyridine 11 4.5 268.0Picric Acid 2,4,6-Trinitrophenol 11 7.4 199.5Styrhnic Acid Trinitroresorcinol 11 7.4 170.6HMX Cyclotetramethylene tetramine 11 7.4 231.4RDX Cyclotrimethylene trinitramine 11 7.5 233.2DINGU Dinitroglycoluril 11 5±6 199.4Hexanitrodiphenyloxid 2,4,6,2

0,40,60-Hexanitrodiphenyloxide 11 8.0 280.4

TNB Ac. Trinitrobenzoic Acid 11 10.0 191.7TNC 2,4,6-Trinitrocresol 11 12.0 163.4TNT 2,4,6-Trinitrotoluene 11 15.0 180.8TNA Trinitroaniline 11 15.0 179.9Trinal Trinitronaphthalene 11 19.0 160.5Trinitroanisole Trinitroanisole 11 20.0 163.1TNMA 2,4,6-Trinitro-N-methylaniline 11 21.2 165.1NTO 3-Nitro-1,2,4-triazole-5-one 12 25.0 132.8Picramic Acid Dinitroaminophenol 11 34.0 109.2DNB Metadinitrobenzene 11 39.0 154.5ClDNB Dinitrochlorobenzene 11 49.0 143.3DNT Dinitrotoluene 11 50.0 127.9TATB 1,3,5-Triamino-2,4,6-trinitrobenzene 11 50.0 125.0ANTA 3-Amino-5-nitro-1,2,4-triazole 12 50.0 111.5NQ Nitroguanidine 11 50.0 76.6

238 M. Vaullerin, A. Espagnacq, and L. Morin-Allory Propellants, Explosives, Pyrotechnics 23, 237±239 (1998)

4. Conclusion

In conclusion, we can say that impact sensitivity for

energetic materials is an athermal phenomenon, that is to

say, the sensitivity criterion CS is based on the most stable

products taken at 298 K.

A parallel can be established with the potential of

ionization and the oxygen balance. The athermal process

of impact sensitivity has only been taken into account

with the potential of ionization. We have found that

the concept of the most stable reaction products is linked

to the oxygen balance. On the other hand the relationship

that exists with the number of atoms per gram is found

in the oxygen balance and in the potential of ioni-

zation.

This comparison with the potential of ionization and the

oxygen balance shows that this new criterion of sensitivity

CS simultaneously unites the three factors: athermal phe-

nomenon, the most stable products of reaction and the

number of atoms per gram, contrary to the notions of

oxygen balance and potential of ionization which elude one

of these three relationships.

Furthermore, results show the superiority of this

approach in comparison with previous works since they

allow the explosives to be classi®ed in interfamilies rather

than intrafamilies. This same criterion can be used for

energetic aluminized, chlorinated . . . formulations. In these

last cases, a hypothetical molecule CaHbOcAldCle . . . has to

be de®ned and the equation of reaction is written with the

most stable products of reaction.

It is obvious that the experimental measures of impact

sensitivity should be carried out the same conditions so as to

establish a homogeneous database because the available

scienti®c literature proposes a mosaic of measures which

are often dif®cult to compare.

5. References

(1) M. J. Kamlet, `̀ The Relationship of Impact Sensitivity withStructure of Organic High Explosives: I. PolynitroaliphaticExplosives'', Proceedings 6th Symposium (International) onDetonation, San Diego, August 1976, ONR Report ACR 221,312±322.

(2) M. J. Kamlet and H. G. Adolph, `̀ The Relationship of ImpactSensitivity with Structure of Organic High Explosives: II. Poly-nitroaromatic Explosives'', Propellants Explos. 4, 30±34 (1979).

(3) W. S. Wilson, D. E. Bliss, S. L. Christian, and D. J. Knight,`̀ Explosive Properties of Polynitroaromatics'', Naval WeaponsCenter, NWC TP 7073.

(4) D. E. Bliss, S. L. Christian, and W. S. Wilson, `̀ Impact Sensitivityof Polynitroaromatics'', J. Energ. Mater. 9, 319±344 (1991).

(5) J. Mullay, (a) `̀ A Relationship Between Impact Sensitivity andMolecular Electronegativity'', Propellants Explos. 12, 60±63(1987). (b) `̀ A Relationship between Impact Sensitivity andElectronic Structure'', Propellants Explos. 12, 121±124 (1987).

(6) A. Delpuech, `̀ Relation entre la structure eÂlectronique moleÂcu-laire et la sensibilite au choc des explosifs secondaires'', TheÁse deDoctorat eÁs Sciences, Universite de Bordeaux (1980).

(7) I. Fukuyama, T. Ogawa, and A. Miyake, `̀ Sensitivity andEvaluation of Explosive Substances'', Propellants Explos. 11,140±143 (1986).

(8) H. Nefati, `̀ PreÂdiction de la sensibilite au choc des substancesexplosives ou non: approches statistique et neuronale'', TheÁse deDoctorat eÁs Sciences, Universite Paris VI (1994).

(9) W. H. Seaton, E. Freedman, and D. N. Treweek, `̀ CHETAH, TheASTM Chemical Thermodynamic and Energy Release EvaluationProgram'', ASTM Data Published Series, Publication DS 51,American Society for Testing and Materials, Philadelphia (1974).

(10) CHETAH, version 7.0, `̀ The Computer Program for ChemicalThermodynamic and Energy Release Evaluation (NIST SpecialDatabase 16)'', 3rd edition, American Society for Testing andMaterials, 1916 Rase Street, Philadelphia, PA 19103 (1994).

(11) J. KoÈhler, and R. Meyer, `̀ Explosives'', VCH, Weinheim (1993).(12) K. Y. Lee, C. B. Storm, M. A. Hiskey, and M. D. Coburn, `̀ An

Improved Synthesis of 5-Amino-3-Nitro-1H-1,2,4-Triazole(ANTA), a Useful Intermediate for the Preparation of InsensitiveHigh Explosives'', J. Energ. Mater. 9, 415±428 (1991).

(Received May 7, 1997; Ms 27y97)

Figure 1. Diagram of interfamily explosive classi®cation.

Propellants, Explosives, Pyrotechnics 23, 237±239 (1998) Prediction of Explosives Impact Sensitivity 239