This paper provides an overview of the main developments over the past nine years in the study of the sensitivity of energetic materials (EM) to impact, shock, friction, electric spark, laser beams, and heat. Attention is also paid to performance and to its calculation methods. Summaries are provided of the relationships between sensitivity and performance, the best representations for the calculation methods of performance being the volume heat of explosion or the product of crystal density and the square of detonation velocity. On the basis of current knowledge, it is possible to state that a single universal relationship between molecular structure and initiation reactivity does not yet exist. It is confirmed that increasing the explosive strength is usually accompanied by an increase in the sensitivity. In the case of nitramines this rule is totally valid for friction sensitivity, but for impact sensitivity there are exceptions to the rule, and with 1,3,5-trinitro-1,3,5-triazepane, 1,3,5-trinitro-1,3,5-triazinane, β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane, and the α-, β- and e-polymorphs of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane the relationship works in the opposite direction. With respect to the QSPR approach there might be reasonably good predictions but it provides little insight into the physics and chemistry involved in the process of initiation.

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Sensitivity and Performance of Energetic Materials

Molecular and crystal designs are crucial to the engineering of high-energy explosives, which are a class of substantial materials usually with high costs and high risks. Understanding their structures, properties, and performances, and the relationships among them is the basis for the design. As a continuation of a systemic analysis of the crystal packing of low-sensitivity and high-energy explosives (LSHEs) (Cryst. Growth Des. 2014, 14, 4703−4713), we present in this work another analysis of 10 existing impact-sensitive high-energy explosives (SHEs), which possess both velocities of detonation and impact sensitivity close to or higher than those of RDX. We find that SHE molecules are usually less stable than LSHE ones, due to the deficiencies of big π-conjugated molecular structures, and adequate and strong intramolecular hydrogen bonds (HBs) even though H atoms are contained. The intermolecular HBs cannot be formed sometimes in H-contained SHE crystals, and the noncovalent O···O interactions dominate t...

Crystal Packing of Impact-Sensitive High-Energy Explosives

Fabrication of RDX, HMX and CL-20 based microcapsules via in situ polymerization of melamine–formaldehyde resins with reduced sensitivity

Recent advances in thermal analysis and stability evaluation of insensitive plastic bonded explosives (PBXs)

Bicyclo-HMX (cis-1, 3, 4, 6-tetranitro-octahydroimidazo-[4, 5-d] imidazole or BCHMX) was studied as a plastic explosive bonded with the C4 matrix and with Viton A. Also a series of nitramines namely RDX (1, 3, 5-trinitro- 1, 3, 5-triazinane), HMX (1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocane) and HNIW (e-2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazaisowurtzitane, e-CL-20) were studied for comparison with the same types of binders. The detonation velocity, D, of all prepared mixtures was measured. Their thermal stability was determined using non-isothermal differential thermal analysis (DTA). While the C4 matrix lowers the thermal stability of the resulting explosives, Viton A enhances this stability. Approximate relationships between the peaks of exothermic decomposition and the D values were found. The detonation parameters were also calculated by means of Kamlet & Jacobs method, CHEETAH and improved EXPLO5 code for all the mixtures. From the measured D values and the calculated detonation parameters, it is obvious that the detonation parameters of BCHMX-mixtures are very close to HMX-explosives and better than those of RDX-mixtures. It was found that the C4 matrix reduces the difference between the values of energy of detonation in the studied C4 mixtures. As expected, the pressed HNIW-Viton A mixture has the highest detonation parameters of all of the prepared mixtures.

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Thermal Stability and Detonation Characteristics of Pressed and Elastic Explosives on the Basis of Selected Cyclic Nitramines

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

At present, cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (bicyclo-HMX, BCHMX) and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, CL-20) are a topic of interest from the attractive and the potentially attainable nitramines. They were chosen to be studied in comparison with 1,3,5-trinitro-1,3,5-triazinane (RDX) and β-1,3,5,7-tetranitro-1,3,5-tetrazocane (β-HMX). Marginal attention is devoted also to 4,8,10,12-tetranitro-2,6-dioxa-tetraazawurtzitane (Aurora 5). BCHMX, e-HNIW, RDX, and HMX were studied as plastic bonded explosives (PBXs) with elastic properties based on Composition C4 and Semtex 10 matrices. Also they were studied as a highly pressed PBXs based on the Viton A binder. The detonation parameters and sensitivity aspects of these nitramines and their corresponding PBXs were determined. Relative explosive strengths (RS) of these compositions are mentioned with mutual relationships between the measured RS values and some detonation parameters. These relationships indicate a possibility of changes in detonation chemistry of these mixtures filled mainly by HNIW. A sensitivity of RS-CL20 (HNIW with reduced sensitivity) is reported and the new findings in the friction sensitivity are discussed.

Attractive Nitramines and Related PBXs

Matrices based on polyisobutylene (PIB), polymethyl-methacrylate (PA), Viton A 200, Dyneon FT 2481 (Fluorel), and polydimethyl-siloxane binders were studied as desensitizers. A series of plastic explosives (PBXs) were prepared, based on four different nitramines, namely RDX (1,3,5-trinitro-1,3,5-triazinane), β-HMX (β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane), BCHMX (cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole) and e-HNIW (e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, e-CL-20), bonded by the matrices mentioned. For comparison, pentaerythritol tetranitrate and certain commercial explosives based on it, Semtex 1A, Semtex 10 and Sprangdeg m/46, were used. Detonation velocities, sensitivities to impact and friction, and peak temperatures of thermal decomposition by differential thermal analysis technique (DTA) for all the explosives studied were determined. Heat of detonation was calculated by means of a thermodynamic calculation program (EXPLO 5 code). Fluoroelastomers have a neutral to positive effect on the thermal stability of nitramines and they have a significant effect on decreasing the friction sensitivity. However, their anti-impact efficiency is the lowest in this study although they have a positive effect on performance of the corresponding PBXs. PA and PIB matrices markedly decrease thermal stability of nitramines, the anti-impact influences of PIB-binders are better than those of PA-binders, while PA-binders have a higher anti-friction effect and slightly less negative influence on the performance of the PBXs in comparison with PIB mixtures. The polydimethyl-siloxane matrix has a neutral effect on thermal stability of the nitramines studied, it has an influence on the volume thermochemistry of detonation comparable with that of fluoroelastomers although it does not provide comparable performance, and its corresponding PBXs have optimum sensitivity parameters.

Effect of Different Polymeric Matrices on Some Properties of Plastic Bonded Explosives

Plastic explosives based on different cyclic nitramines with different polymeric matrices were prepared and studied. The used polymeric matrices were fabricated on the basis of polyisobutylene (PIB), acrylonitrile-butadiene rubber (ABR), Viton A, and polydimethyl-siloxane as binders, whereas the nitramines named RDX (1,3,5-trinitroperhydro-1,3,5-triazine), β-HMX (β-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), BCHMX (cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole) and e-HNIW (e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) were used as explosive fillers. Commercial Semtex 10, based on pentaerythritol tetranitrate (PETN), was used for comparison. Impact sensitivity, loading density, ρ, detonation velocity, D, and relative explosive strength (RS) measured by ballistic mortar were determined. It was concluded that plastic BCHMX based on Viton A or PIB-matrix exhibits higher RS compared with PBXs based on RDX and HMX. Correlations between RS and the impact sensitivity, the ρD2 term and the square of the detonation velocity were studied and discussed. The results confirm the well-known fact that increasing the performance is usually accompanied by an increase in the sensitivity of the explosives. In this connection, Viton A enables achieving a high RS, but with a relatively high sensitivity of the PBXs, whereas the polydimethyl-siloxane matrix should perhaps give PBXs with optimum explosive strength and sensitivity parameters.

Marcela Jungová

Papers

Sensitivity and Performance of Energetic Materials

cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), its properties and initiation reactivity

Attractive Nitramines and Related PBXs

Effect of Different Polymeric Matrices on Some Properties of Plastic Bonded Explosives

Explosive Strength and Impact Sensitivity of Several PBXs Based on Attractive Cyclic Nitramines