Study of initiation reactivity of some plastic explosives by vacuum stability test and non-isothermal differential thermal analysis

An attempt was made to develop a general description of impact sensitivity. For this purpose a set of 24 well-known, as well as recently synthesized, C–H–N–O–Cl explosives covering the wide range of impact sensitivity (h50 = 9–320 cm) was studied using first-principles calculations at different external pressures. To quantify impact sensitivity, a theoretical approach was developed based on the solid-state derived criteria, which include triggering pressure, average number of electrons per atom, crystal morphology, energy content and melting temperature. These criteria follow from the theoretical consideration of the crystal compression caused by an impact event. Apart of the compression, the influence of crystal habit shapes and energy content are also discussed. The main idea is in the electron flow probability from valence to conduction bands in a solid. To support the developed theoretical background, the corresponding numerical illustration is presented in the paper. The obtained empirical correlatio...

Quantification of Impact Sensitivity Based on Solid-State Derived Criteria

Quantitative results are presented for the formation of two nitroso compounds during the drop-weight impact of Holston production-grade Class D RDX explosive crystals. Gas chromatography, using a sensitive Ni-63 electron capture detector, was employed to analyze “RDX residues” recovered from impact tests involving a 5 kg mass dropped from 10, 12, and 14 cm heights. The compounds, 1,3,5-trinitroso-1,3,5-triazacyclohexane (R) and 1,3-dinitroso-5-nitro-1,3,5-triazacyclohexane (RO) were detected at levels of (0·80 to 9·3) × 10−10 percent and (1·3 to 560) × 10−10 percent, respectively. More RO than R was formed at the 14 cm drop height. This appears to be the first time that nitroso compounds structurally similar to RDX have been observed in impacted RDX crystals.

Quantitative evidence for nitroso compound formation in drop-weight impacted RDX crystals

In heavily irradiated NaCl explosions can be initiated during irradiation or later, after the irradiation, when the samples are heated to temperatures in the range 100–250°. As a result of the irradiation Na and Cl2 precipitates, dislocations and voids are produced, along with stored energy (the maximum value observed until now ∼ 76kJ/mol, which is about 18.5% of the enthalpy of formation of NaCl, 411.2kJ/mol). This implies that heavily irradiated NaCl is a highly energetic material. We have observed that the samples, which revealed large radiation-induced voids, explode rather easily. In these samples the instability connected with large voids (hot spots) probably initiates the explosive release of stored energy, which is in many cases accompanied by characteristic (explosive) sounds. In this paper we will discuss the nature of the explosions and show that a basically stable insulating compound, such as NaCl, may become unstable after heavy irradiation.

/pdf/explosive-decomposition-of-heavily-irradiated-nacl-162h37h7ha.pdf

Explosive decomposition of heavily irradiated NaCl

Determination of adiabatic ionization potentials and electron affinities of energetic molecules with the Gaussian-4 method

Efforts to generate detectable concentrations of free radicals in explosives, binders, and their mixtures are described. Radicals were readily produced in polycaprolactone and polyethylene glycol binders at liquid nitrogen temperature using stresses as low as 0.4 kbar. These radicals were all of the peroxy type, and presumably formed by reaction of mechano-radicals with oxygen present in the polymer. No mechano-radicals were observed from HMX or RDX using samples cooled to liquid nitrogen temperature and applied stresses up to 4 kbar. In neither impacted samples that failed to explode nor the residues remaining after a partial explosion were radicals detected by ESR.

Low temperature γ-irradiation of these materials was also carried out. Free radical signals originating in both the polymer and the explosive could be identified. The reactivity of NO2 radicals from γ-irradiated HMX is enhanced in the presence of binder. In γ-irradiated HMX/polycaprolactone mixtures, the NO2 radical anneals rapidly at 150 K, versus 240 K for HMX alone.

Evidence is presented to suggest that the relatively stable NO2 radical (such as produced by γ-irradiation) in HMX does not play a dominant role in mechanical initiation.

Generation of Free Radicals in RDX and HMX Compositions

Impact of thin layers of HMX at room temperature and near liquid nitrogen temperature were performed. Polycrystalline powders of HMX irradiated with 7.5 megarad in evacuated tubes at liquid nitrogen temperature showed significant enhanced sensitivity. With 10-megarad irradiations of HMX in evacuated tubes at liquid nitrogen temperature frequent spontaneous explosions in HMX have occurred. ESR measurements on impacted HMX and RDX powders at room temperature and near liquid nitrogen temperature at energies of less than 1 kg · m have not produced detectable mechanically generated free radicals. A significant increase in sensitivity of vacuum irradiated HMX was observed but efforts to correlate this with the dominant frozen-in NO2 γ-radical concentration were unsuccessful. It is suggested that the NO2 radical is a chain terminating radical in explosive systems.

Impact Sensitivity of γ-Irradiated HMX

Internal friction measurements of zone‐refined Al were obtained up to pressures of 5 kbar. The log of the background damping was found to increase linearly with pressure, with slopes of about 1.5×10−4 kbar−1 and 47.7×10−4 kbar−1 for CS2 and kerosene pressure media, respectively. A reversible, intrinsic, pressure dependence of the amplitude‐dependent part of the decrement Δ was found for Al of the approximate form ∂(lnΔ)/∂p = M+N/e0, where M = −4.5×10−3 kbar−1, N = −4.2×10−8 kbar−1, and e0 is the strain amplitude. Theoretical expressions for the value of the ``misfit parameter'' e′ and its pressure derivative are derived from the Granato‐Lucke theory in terms of M, N, and elastic constant data. It is suggested that the Granato‐Lucke theory does not apply to zone‐refined Al at these strain amplitudes.

M. H. Miles

Papers

Generation of Free Radicals in RDX and HMX Compositions

Impact Sensitivity of γ-Irradiated HMX

Internal Friction under Hydrostatic Pressure