Review of Phase Transformations in Energetic Materials as a Function of Pressure and Temperature

Abstract

Under ambient conditions, energetic materials may exist in one or more than one metastable crystal structure. Under compression or when heated, the material may transform into a different structure or may decompose. Mapping the phase diagram of explosive materials at high pressures and temperatures is an important component to evaluate their performance and safety aspects. In particular, a detailed knowledge of polymorphism and the structural and chemical stabilities of the various phases is necessary to understand the reactive behavior of explosive materials in the high-pressure and high-temperature range that is relevant to shock-wave initiation. Phase transformations could be rate-dependent; that is, fast compression or rapid heating could result in different transformation pressures, temperatures, or even structures compared with static compression and slow heating because shock compression could be accompanied by sudden and extreme heating effects. Nevertheless, static methods are expected to give a fair idea of the structure of the materials under different P–T conditions and, from the structure, their performance characteristics. Also, the shock-wave physics and chemistry of explosives are so complex that in shock experiments it has not been possible to identify the intermediate phases of molecules during decomposition. Hence experiments with static high pressure and high temperature are necessary to gain insight into these processes. Additionally, computational modeling and simulations have been extensively used to understand the effects of pressure on explosives. There is considerable literature on these aspects of energetic materials accumulated over the years. We will review the current status of experimental results, primarily using X-ray diffraction, Raman, and infrared spectroscopies, as probes exploring the P–T phase diagram of important secondary explosives ammonium nitrate, TNT, TATB, PETN, RDX, HMX, CL-20, TEX, FOX-7, and TKX-50.

The role of electric field on decomposition of CL‐20/HMX cocrystal: A reactive molecular dynamics study

“…Moreover, electric spark, important to the safety of EM due to its wide existence, is usually accompanied by strong EF, 25 yet the role of EF in the initiation of an explosive by electric spark remains unclear. 26 Thus it is of utmost importance to investigate the role of EF in the decomposition of EMs as well as the underlying mechanism.…”

Polymorphic Transition in Traditional Energetic Materials: Influencing Factors and Effects on Structure, Property, and Performance

“…41−46 For instance, Miller and Garroway reviewed the crystal structures of the traditional ECs RDX, HMX, TNT, PETN, and tetryl, 41 the experimental techniques for PT and high-pressure phases of ECs were detailed in a monograph by Peiris and Gump, 42 Millar focused upon the ECs under extremes, with high-temperature and highpressure-induced PT, 43 Pulham et al also reviewed the hydrostatic pressure induced PT of RDX, HMX, CL-20, and FOX-7, 44 Xu et al summarized the experimental techniques for inducing and determining the PT of ECs, with molecular and crystal structures, 45 and very recently, Ravindran et al reviewed the pressure-and temperature-induced PT of TNT, TATB, PETN, RDX, HMX, CL-20, 4,10-dinitro-2,6,8,12-tetraoxa-4,10diazaisowurtzitane (TEX), FOX-7, and dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50). 46 The aforementioned reviews mainly focused upon the crystal structure and the conditions for the PT: i.e., the increased temperature and pressure. As illustrated in Figure 2, we will present an overall perspective of the relatives of the polymorphism and PT of TNT, PETN, RDX, HMX, CL-20, and FOX-7, including not only the scientific insights into the PT mechanism but also the strategies for engineering applications.…”

“…Up to the present, some works have reviewed the progress in finding new crystalline phases of ECs. − For instance, Miller and Garroway reviewed the crystal structures of the traditional ECs RDX, HMX, TNT, PETN, and tetryl, the experimental techniques for PT and high-pressure phases of ECs were detailed in a monograph by Peiris and Gump, Millar focused upon the ECs under extremes, with high-temperature and high-pressure-induced PT, Pulham et al also reviewed the hydrostatic pressure induced PT of RDX, HMX, CL-20, and FOX-7, Xu et al summarized the experimental techniques for inducing and determining the PT of ECs, with molecular and crystal structures, and very recently, Ravindran et al reviewed the pressure- and temperature-induced PT of TNT, TATB, PETN, RDX, HMX, CL-20, 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane (TEX), FOX-7, and dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) …”

High‐Pressure Characterization of the Cage‐Structured Explosive TEX by Dispersion‐Corrected DFT Calculations

“…As we all know, hexanitrohexaazaisowurtzitane (HNIW, also known as CL‐20) is the densest N ‐nitramine explosive. [ 10 ] The high density of CL‐20 greatly depends on the isowurzitane cage structure in this compound. Similar to CL‐20, 4,10‐Dinitro‐2,6,8,12‐tetraoxa‐4,10‐diazaisowurtzitane (TEX), is also a cage‐structured explosive.…”

“…Namely, the skeleton is a rigid isowurtzitane cage that includes a six‐membered ring and two five‐membered rings. [ 10,12–16 ] Due to the absence of sterically demanding nitramine groups in the TEX molecular structure, TEX is an insensitive explosive.…”