Pentaerythritol Tetranitrate Single Crystals Research Articles

A reactive flow simulation for the anisotropic ignition of an explosive crystal using adaptive mesh refinement

In this study, we consider the anisotropic or direction-dependent ignition of single crystal pentaerythritol tetranitrate (PETN). Previous experiments have shown that the anisotropic ignition of PETN is induced by the crystal orientation and micro-structural features at the molecular scale. Numerical models have taken the standard approach of considering only the isotropic ignition via ignition and the growth process, which assume a perfect isotropy or orientation independence for the ignition of an explosive crystal. Based on our previously announced anisotropic concept, which depends on strain and the strain rate, we developed an adaptive mesh refinement technique to carry out three-dimensional simulations of the anisotropic ignition of a PETN crystal subjected to directional shock loadings.

Extended asymmetric hot region formation due to shockwave interactions following void collapse in shocked high explosive

In both continuum hydrodynamics simulations and also multimillion atom reactive molecular dynamics simulations of shockwave propagation in single crystal pentaerythritol tetranitrate (PETN) containing a cylindrical void, we observed the formation of an initial radially symmetric hot spot. By extending the simulation time to the nanosecond scale, however, we observed the transformation of the small symmetric hot spot into a longitudinally asymmetric hot region extending over a much larger volume. Performing reactive molecular dynamics shock simulations using the reactive force field (ReaxFF) as implemented in the LAMMPS molecular dynamics package, we showed that the longitudinally asymmetric hot region was formed by coalescence of the primary radially symmetric hot spot with a secondary triangular hot zone. We showed that the triangular hot zone coincided with a double-shocked region where the primary planar shockwave was overtaken by a secondary cylindrical shockwave. The secondary cylindrical shockwave originated in void collapse after the primary planar shockwave had passed over the void. A similar phenomenon was observed in continuum hydrodynamics shock simulations using the CTH hydrodynamics package. The formation and growth of extended asymmetric hot regions on nanosecond timescales has important implications for shock initiation thresholds in energetic materials.

New insights into kinetics of PETN decomposition from the product and reactant point of view: An investigation with mass spectrometry and differential scanning calorimetry

Pentaerythritol tetranitrate (PETN) is a benchmark organic energetic material and is used in both military and industrial applications. Accurate kinetic parameters for the decomposition of energetic materials are required to predict the hazards, thermal cook-off and properties of PETN. Kinetic parameters of PETN decomposition have been previously reported in wide range of values. We are attempting to find new insights on the kinetics of PETN decomposition by studying kinetics of gas evolution and heat released from the reaction. Gas evolution kinetics is studied by a mass spectrometer coupled with a thermogravimetric analyzer (TGA-MS) and heat released in the reaction with a deferential scanning calorimeter (DSC) in open and closed pan. PETN single crystals are used as the samples. The activation energy of decomposition is obtained as a function of extent of reaction by the isoconversional kinetic analysis. The activation energy for the generation of NO2 (m/z=46) in PETN decomposition is consistent with the bond energy of RONO2 in nitrate esters. The activation energy for the overall PETN decomposition is similar to that of the generation of NO2. The effect of confinement on the decomposition kinetics in TGA-MS and DSC, are also discussed in this work. This investigation shows that activation energy for PETN decomposition is in the range of 170–176kJ/mol.

A direction sensitive detonation model for granular to continuum scale for shock initiation of pentaerythritol tetranitrate single crystal in multi-dimensions

Experiments have shown that the shock sensitivity of a single crystal pentaerythritol tetranitrate (PETN) has a strong dependence on the crystal orientation. The ignition and growth (I & G) model has been widely used in studies of the shock initiation of energetic materials while the model is independent of the direction of compression, and thus it is impossible to address anisotropic sensitivity of such material. In this paper, we base our new model in the recently proposed reactive flow concept that incorporates an anisotropic ignition mechanism that depends on both strain and strain rate which are given in the general tensor notation. A multi-dimensional simulation is performed in order to illustrate the strain dependence of the initiation of a PETN pellet. The model is applicable to any anisotropic energetic material subjected to a shock impact, not limited to single crystal PETN.

Controlling the coarsening stability of pentaerythritol tetranitrate (PETN) single crystals by the use of water

The surface area of the secondary explosive pentaerythritol tetranitrate (PETN) affects its initiation and performance. A decrease in the surface area, as well as morphology changes, in PETN has been observed during aging. Commercially, water is used in the production of PETN which suggests an uninvestigated stability control factor. In this article, single crystals of PETN were grown by solvent evaporation method from acetone at room temperature in absence and presence of different weight ratios of de-ionized water. The effect of presence of water in the starting solution of PETN on its thermodynamic properties was investigated using thermogravimetric analysis and differential scanning Calorimetry. The TGA study suggests an important role for water in manipulating thermodynamic parameters of PETN via the expected hydrogen bonding. The DSC results suggest the presence of bound water molecules as impurity in PETN single crystals. The data could be used to form PETN crystals with desired physical properties optimal for either storage or initiation. This study suggests that, in the equilibrium conditions, water could be used in a cheap, tunable, and precise manner to control the stability of PETN crystals against coarsening.

Orientation Dependent Far-Infrared Terahertz Absorptions in Single Crystal Pentaerythritol Tetranitrate (PETN) Using Terahertz Time-Domain Spectroscopy

Terahertz time-domain spectroscopy (THZ-TDS) has been used to measure the absorption spectra in the range 7-100 cm(-1) (0.2-3 THz) of single crystal pentaerythritol tetranitrate (PETN). Absorption was measured in transmission mode as a function of incident polarization with the incident and transmitted wave vectors oriented along the crystallographic directions [100], <10(a/c)(2)>, and <110>. Samples were rotated with respect to the incident polarization while absorption was measured at both 300 and 20 K. Comparatively minor differences were observed among the three orientations. Two broad absorptions at 72 and >90 cm(-1), and several weaker absorptions at 36, 55, 80, and 82 cm(-1), have been observed at cryogenic temperatures.

A comparative evaluation of elasticity in pentaerythritol tetranitrate using Brillouin scattering and resonant ultrasound spectroscopy

Elastic tensors for organic molecular crystals vary significantly among different measurements. To understand better the origin of these differences, Brillouin scattering and resonant ultrasound spectroscopy measurements were made on the same specimen for single crystal pentaerythritol tetranitrate. The results differ significantly despite mitigation of sample-dependent contributions to errors. The frequency dependence and vibrational modes probed for both measurements are discussed in relation to the observed tensor variance.

Shock Wave Induced Decomposition Chemistry of Pentaerythritol Tetranitrate Single Crystals: Time-Resolved Emission Spectroscopy

The decomposition mechanism in shocked pentaerythritol tetranitrate (PETN) was examined using time-resolved emission spectroscopy. PETN single crystals were subjected to stepwise loading along [100] and [110] to peak stresses between 2 and 13 GPa. Due to concurrent changes in the optical transmission of PETN, emission spectra were analyzed using the absorption data acquired separately under the same loading conditions. Analyses of the corrected emission data revealed two bands in the spectra at ∼3.0 and ∼2.4 eV. Both bands were observed in every experiment regardless of stress or crystal orientation. However, their relative and absolute intensities, and temporal behavior revealed stress and orientation dependence. The emission was identified as chemiluminescence from the nitronium ion, NO2+, on the basis of its electronic structure and properties. NO2+ electronic structure was analyzed using ab initio calculations, which showed transition energies matching those of the emitting intermediate observed exper...

Dynamic elastic-plastic properties of single-crystal pentaerythritol tetranitrate

The dynamic elastic-plastic behavior of single crystals of the secondary explosive pentaerythritol tetranitrate (PETN) have been studied at input shock strengths between 0.6 and 4.0 GPa (6–40 kbar). Crystals with surfaces cut perpendicular to the 〈110〉 and 〈001〉 directions were struck by gas-gun projectiles and stress histories at both sample faces were determined with quartz dynamic stress gauges. The amplitude of the elastic wave increases markedly with input shock strength and decreases with distance of run. A viscous relaxation model based on the theory of dislocation dynamics is consistent with the observations and yields estimates of 6.8 GPa μs (6.8×104 P) for the dynamic viscosity at the shock front and 1.1×1010 m−2 for the dislocation density. Observed impact-face shock states correspond to the hydrostat Hugoniot, suggesting that little shear stress is retained after yielding begins. With input shock strengths of 4.0 GPa, pressure buildup at the impact face is observed, indicating energy relase near this surface. This occurs at about half the input shock strength that would be expected from previous initiation experiments and theoretical calculations on single-crystal PETN.