The response of the HMX-based material PBXN-9 to thermal insults: thermal decomposition kinetics and morphological changes Page: 3 of 18
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The response of the HMX-based material PBXN-9 to thermal insults: thermal
decomposition kinetics and morphological changes
Elizabeth A. Glascoea*, Peter C. Hsua, H. Keo Springers, Martin R. DeHavena, Noel Tana, Heidi C. Turner
a Energetic Materials Center, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550
*Corresponding Author. Tel.: +1 925 424 5194; fax: +1 925 424 3281; E-mail address: email@example.com
PBXN-9, an HMX-formulation, is thermally damaged and thermally decomposed in order to determine the
morphological changes and decomposition kinetics that occur in the material after mild to moderate heating. The
material and its constituents were decomposed using standard thermal analysis techniques (DSC and TGA) and the
decomposition kinetics are reported using different kinetic models. Pressed parts and prill were thermally damaged,
i.e. heated to temperatures that resulted in material changes but did not result in significant decomposition or
explosion, and analyzed. In general, the thermally damaged samples showed a significant increase in porosity and
decrease in density and a small amount of weight loss. These PBXN-9 samples appear to sustain more thermal
damage than similar HMX-Viton A formulations and the most likely reasons are the decomposition/evaporation of a
volatile plasticizer and a polymorphic transition of the HMX from f to 6 phase.
Thermal damage, thermal decomposition, kinetics, HMX, PBXN-9
A thorough understanding of the response of energetic materials to heat is of broad interest to the explosives
and propellants communities. The development of safe handling and storage methods requires a detailed
understanding of how a material changes when exposed to heat. Mild heating of an explosive may produce
morphological and/or compositional changes that may alter the microstructure and increase material surface area
due to the introduction of voids and pores. These changes can affect the material properties such as sensitivity,
safety, and performance; hence handling and reusing a damaged explosive requires careful consideration. A prior
knowledge of how the material behaves when heated would allow workers to make more informed decisions about
how to deal with a thermally damaged material. In addition, a basic understanding of thermally induced changes
assists in the interpretation of more complex experiments such as deflagration, shock and/or impact initiation
experiments, and thermal explosions. Finally, quantitative characterization of materials after mild heating and
development of decomposition kinetic models provides the data necessary to develop and/or parameterize
computational models used to predict phenomenon such as thermal explosion, shock or impact initiation, sample
The kinetics and mechanisms of thermal decomposition of energetic materials are particularly important to the
study of thermal explosions (e.g. cook-off). A material might explode if it is exposed to a stimulus sufficient to
initiate significant material decomposition, typically the stimulus is heat. In most slow cook-off scenarios, the first
step is molecular-level decomposition via a mechanism that begins with one or more endothermic and/or exothermic
reactions. The decomposition is accelerated by autocatalytic chemical reactions and the energy released due to
exothermic reactions. Eventually the material begins to deflagrate (i.e. burn) and consumption of the material
accelerates. Some materials shift from deflagration to detonation (DDT), yet even materials that do not undergo
DDT can react quite violently, as has been observed in one-dimensional-time-to-explosion (ODTX) and scaled-
thermal-explosion (STEX) experiments [1, 2].
The energetic material HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) is a common molecule used in a
variety of different explosives; consequently, there is a considerable volume of literature investigating the response
of HMX based materials to heat [3-8]. At approximately 160 C, HMX experiences a polymorphic transition, from
the 3- to the 8-polymorph . Because the 8-polymorph is approximately 7% larger in volume the explosive charge
may experience irreversible volume expansion and a significant increase in sample porosity due to irreversible
rearrangement of the crystal-binder packing . These changes in morphology can change the performance of the
Released for public Audience
Published in Thermochimica Acta, 515 (2011) 58-66.
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Glascoe, E A; Hsu, P C; Springer, H K; DeHaven, M R; Tan, N & Turner, H C. The response of the HMX-based material PBXN-9 to thermal insults: thermal decomposition kinetics and morphological changes, article, December 10, 2010; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc832711/m1/3/: accessed July 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.