Class Of Energetic Materials Research Articles

Theoretical study on the trans– cis isomerization and initial decomposition of energetic azofurazan and azoxyfurazan

In this work, we carried out the hybrid density functional theory (DFT) calculations in order to understand the thermal trans– cis isomerization and initial thermal decomposition of 3,3′-diamino-4,4′-azofurazan (DAAzF), 3,3′-diamino-4,4′-azoxyfurazan (DAAF), 3,3′-dinitro-4,4′-azofurazan (DAAF) and 3,3′-dinitro-4,4′-azoxyfurazan (DAAzF). The relative energy between the trans- and cis-isomer was also calculated at the B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level of theory. We found that a negative correlation existed between the relative energy and the sensitivity for these energetic azofurazan and azoxyfurazan compounds, where the higher relative energy means the lower the sensitivity. It was also found that the oxidation of azo-group could cause the decreasing in the relative energy between the trans- and cis-isomer, as well as the alteration of the isomerization mechanism. An inversion mechanism operates for azofurazan compounds (DAAzF and DNAF) while a rotation mechanism works for azoxyfurazan compounds (DAAF and DNOAF). Compared with the thermal trans– cis isomerization, the homolytic cleavage of C–N bond needs to overcome a much higher energy barrier, which indicates that the energy of the external stimulus should firstly trigger the trans– cis isomerization, rather than the breakage of C–N bond. A self-desensitization effect caused by the reversible thermal trans– cis isomerization process was firstly proposed to explain that the azofurazan and azoxyfurazan compounds are class of energetic materials with lower sensitivity. This new concept (self-desensitization effect) is expected to be useful to design the novel high density, insensitive energetic material.

Reaction Propagation of Four Nanoscale Energetic Composites (Al/MoO3, Al/WO3, Al/CuO, and B12O3)

Nanoscale composite energetics (also known as metastable intermolecular composites) represent an exciting new class of energetic materials. Nanoscale thermites are examples of these materials. The nanoscale thermites studied consist of a metal and metal oxide with particle sizes in the 30-200 nm range. They have potential for use in a wide range of applications. The modes of combustion and reaction behavior of these materials are not yet well understood. This investigation considers four different nanoaluminum/metal-oxide composites. The same nanoscale aluminum was used for each composite. The metal oxides used were molybdenum oxide (MoO 3 ), tungsten oxide (WO 3 ), copper oxide (CuO), and bismuth oxide (Bi 2 O 3 ). The reaction performance was quantified by the pressure output and propagation velocity using unconfined (or open burn) and confined (burn tube) experiments. We examine the optimization of each composite in terms of pressure output and propagaton speed (or burn rate) for the open burn experiment. We find that there is a correlation between the maximum pressure output and optimum propagation speed (or burn rate). Equilibrium calculations are used to interpret these results. We find that the propagation speed depends on the gas production and also on the thermodynamic state of the products. This suggests that condensing gases or solidifying liquids could greatly enhance heat transfer. We also vary the density of these composites and examine the change in performance. Although the propagation wave is likely supersonic with respect to the mixture sound speed, the propagation speed decreases with density. This behavior is opposite of classical detonation in which propagation (detonation) speed increases with density. This result indicates that the propagation mechanism may differ fundamentally from classical detonations.

Energy Release Characteristics of Impact-Initiated Energetic Materials

AbstractImpact-initiated energetic materials are a class of energetic materials that are formulated to release energy under highly dynamic loads. Under quasi-static or static loads, however, the materials are intended to be inert and carry a material classification of 4.1 flammable solid. In general, these materials are formed by introducing metal powders into a polymer binder but a number of binderless varieties exist (primarily pressed/sintered intermetallics and thermites). Most of the materials are sufficiently insensitive so as not to produce a self-sustaining reaction; as such, they require the mechanical work of a high-strain-rate plastic deformation process to provide the energy required to drive the reaction. Traditional initiation techniques such as exploding bridge wires or flame initiation are not sufficient to maintain a reaction in this class of materials. This paper presents a brief overview of the energy release characteristics of this class of materials, including a discussion of the material formulations, initiation phenomena, and a discussion of the manner in which the material properties affect the energy release characteristics.

Method for estimating decomposition characteristics of energetic chemicals

AbstractExperimental data on the decomposition characteristics of approximately400 chemicals, representing various classes of energetic materials, were summarized by chemical class and statistically analyzed. Average decomposition characteristics, such as energy of decomposition and decomposition onset temperature, were determined for chemical classes containing the following energetic groups: nitro, nitroso, N‐oxide, oxime, hydroxylamine, tetrazole, azide, triazene, triazole, diazo, azo, hydrazine, and perchlorate. Additional statistical information is presented for each chemical class, such as number of chemicals analyzed, ranges, and standard deviations for the decomposition parameters analyzed. For chemical classes containing an energetic group attached to an aromatic ring, the presence and position of another substituting group in the ring can significantly influence the decomposition onset temperature. The study summarizes the list of activating and deactivating functional groups, and the positions in the ring where the strongest activation or deactivation occurs. The authors also recommend a method for estimating decomposition parameters of new chemicals.

A detailed model for the decomposition of nitramines: RDX and HMX

A unified decomposition scheme for two very important cyclic nitramines used as primary explosives – RDX and HMX – has been constructed using ab initio Density Functional Theory (DFT) calculations. Molecular parameters such as vibrational frequencies and moments of inertia corresponding to the computed potential energy profile of unimolecular decomposition of these nitramines were then used to obtain the thermochemistry of all identified species and reaction rate constants of each individual channel. These primary decomposition reactions were then combined with: (i) important secondary reactions of the key reactive radical intermediates, such as CH2NNO2 (Methylene Nitramine MN), CH2N, NO, NO2, OH, etc.; (ii) existing nitramie reaction networks [33]. We have developed an improved mechanism for the detailed chemistry of nitramines which can be applied to combustion and detonation phenomena of this class of energetic materials.

Gas production from thermal decomposition of explosives: Assessing the thermal stabilities of energetic materials from gas production data

The gas formation associated with the thermal decompositions of nineteen energetic materials was determined at three temperatures (120°C, 220°C and 320°C). Although there was considerable variability within classes, among the largest producers of gas were the nitrate esters. PETN (pentaerythritol nitrate) generated about 6.3mole gas per mole, while nitrocellulose, produced almost no gas. Second in gas production were the nitramines, followed by nitroarenes and lastly, energetic salts. NTO (5-nitro-2, 4-dihydro-3H-1, 2, 4-triazol-3-one), which does not fit into the four main classes of energetic materials, exhibited gas production (2.13 mole gas per mole NTO) comparable with some nitroarenes and the energetic salt, ammonium dinitramide (ADN). For selected compounds gas evolution data was used to construct first-order plots, from which Arrhenius parameters were determined and compared with previously reported values.

A thermochemical model for shock-induced reactions (heat detonations) in solids

Recent advances in studies of shock-induced chemistry in reactive solids have led to the recognition of a new class of energetic materials which are unique in their response to shock waves. Experimental work has shown that chemical energy can be released on a time scale shorter than shock-transit times in laboratory samples. However, for many compositions, the reaction products remain in the condensed state upon release from high pressure, and no sudden expansion takes place. Nevertheless, if such a reaction is sufficiently rapid, it can be modeled as a type of detonation, termed ‘‘heat detonation’’ in the present paper. It is shown that unlike an explosive detonation, an unsupported heat detonation will decay to zero unless certain conditions are met. An example of such a reaction is Fe2 O3 +2Al+shock→Al2 O3 +2Fe (the standard thermite reaction). A shock-wave equation of state is determined from a mixture theory for reacted and unreacted porous thermite. The calculated shock temperatures are compared to experimentally measured shock temperatures, demonstrating that a shock-induced reaction takes place. Interpretation of the measured temperature history in the context of the thermochemical model implies that the principal rate-controlling kinetic mechanism is dynamic mixing at the shock front. Despite the similarity in thermochemical modeling of heat detonations to explosive detonations, the two processes are qualitatively very different in reaction mechanism as well as in the form the energy takes upon release, with explosives producing mostly work and heat detonations producing mostly heat.