RDX Powder Research Articles

Hybrid Continuum and Multi‐Particle Simulation of RDX Powder Subjected to Drop Impact

AbstractA variety of energetic material (EM) devices could be designed more efficiently with a more rapid protocol of modeling and testing if computational tools are more predictive. Drop weight impact tester (DWIT) is widely used to experimentally study energetic material response to impact. Drop weight impact on a thin layer of RDX powder is studied here and computationally modeled to compute the likelihood of EM powder ignition from low‐speed impact. The overall objective is to develop a thermomechanical‐based FEM methodology that can qualitatively predict ignition‐likelihood to study iginition mechanics in EM powders and understand how anvil properties and striker impact conditions influence it. The mechanical confinement conditions offered by an anvil and striker type, influence energy transmission and heat localization within the energetic powder. Efficiently modeling both the bulk behavior and the mesoscopic behavior, such as, localized shear and particle‐to‐particle frictional heating, is necessary to design insensitive EM‐devices. A 3D finite element modeling (FEM) approach is described that more accurately models the impact conditions than previously developed 2D models. The results are compared with the experimental results and the 2D simulations. A continuum‐based explicit FEM can only simulate the bulk‐behavior of the powder. To accurately predict hot‐spot ignition mechanisms, meso‐scale multi‐particle models of the EM is needed. For computational efficiency, hybrid models that combines continuum and multi‐particle FEM (MPFEM) were utilized. The computed temperature profiles are compared for two anvil types and demonstrates that an assessment of ignition likelihood is viable with the hybrid methodologies proposed.

Bicyclic High-Energy and Low-Sensitivity Regioisomeric Energetic Compounds Based on Polynitrobenzene and Pyrazoles

With the development of synthetic methodology and crystallography of energetic materials, regiochemistry is becoming popular and vital in the design of versatile energetic compounds as well as in the thorough research on the relationship between structure and property. In this study, two regioisomeric bicyclic energetic compounds based on pyrazole and polynitrobenzene were synthesized simultaneously by a simple synthetic route, and the regioisomers could be purified by a facile approach. It is interesting to note that the ratio of the two compounds changed with temperature. From 80 to 110 °C, the proportion of compound 2 gradually enhanced with the increase in temperature. In addition, the nitramine product of compound 1 was also synthesized. The structural data of compounds 1, 2, and 3 were confirmed by X-ray single-crystal diffraction. The detonation velocities of the new compounds are in the range of 8436–8788 m s–1 and impact sensitivities are between 15 and 27.5 J, of which compounds 2 and 3 not only present superior sensitivities to those of the classical high-energy explosive RDX (7.5 J) but also exhibit comparable detonation velocities to the measured RDX powder (VD = 8796 m s–1), calculated by EXPLO5 as 8788 and 8526 m s–1, respectively. Moreover, compounds 1 and 2 show good thermal stability with decomposition temperatures up to 263 and 287 °C, which is higher than that of RDX (Tdec: 204 °C). All of the above information indicates that these compounds are high-energy, low-sensitivity energetic materials featuring prospective applications.

Qualitative assessment of air pollution in the working area of energy-intensive materials production by nanoscale aerosols with a solid dispersed phase

The presence of grinding, mixing, and fractionation of solid components of formulations leads to the formation of aerosols in the air of the working area with a wide range of dispersion of the solid phase - all this characterizes the organization of technological processes for the production of energy-intensive materials. The study aims to give a qualitative assessment of possible air pollution of the working area of energy-intensive materials production by nanoscale aerosols with a solid dispersed phase. The researchers carried out the sampling of the working area air and flushes from solid horizontal surfaces to produce energy-intensive materials. We carried out the sampling by forced circulation of the test air through the absorption devices of Polezhaev. Scientists used Triton TX-114 solution with a mass concentration of 2.0 mg/dm3 as an absorption medium. The researchers performed flushing from surfaces using cloth tampons moistened with Triton TX-114 solution with a mass concentration of 2.0 mg/dm3. We determined the particle sizes in the samples using NanotracULTRA (Microtrac). Scientists found aluminum and nitrocellulose particles with sizes from 36 to 102 nm in the air of the working area and flushes from horizontal surfaces. The study of the fractional composition of RDX and aluminum powders of the ASD-1 brand showed the presence of nanoscale particles in them. Nanoscale dust particles pollute the air of the working area and solid horizontal surfaces at certain stages of the production of energy-intensive materials. There are nanoscale particles in the composition of powders of some standard components of formulations. Flushes from solid horizontal surfaces are an adequate qualitative indicator of the presence of nanoaerosols in the air of the working area.

Modeling and Simulation of RDX Powder Thermo‐Mechanical Response to Drop Impact

AbstractA computational framework to predict the deformation, flow, and compaction of an energetic material (EM) powder subjected to drop impact is discussed. Explicit dynamic finite element analysis was performed to simulate drop‐weight impact tests for comparison with experimental results and to gain insight into the ignition sensitivity of RDX powder. The computations simulated the Thermo‐Mechanical behavior of a thin layer of energetic powder subjected to drop impact to study the dependence of ignition sensitivity on the anvil material properties. By modeling high strength steel and a low strength copper anvil, a direct comparison is made on how energy dissipation within the EM is influenced by anvil properties. A hybrid finite element model is introduced that captures the mesoscale discrete particle nature of the powder response in regions of interest while using a continuum model elsewhere to reduce computational cost. To capture the mesoscale behavior, a multi‐particle finite element method (MPFEM) approach was used in selected regions in the hybrid model. Powder temperatures were computed to understand how the striker impact energy is dissipated by plasticity and friction into localized heating of the EM that triggers the ignition. Munition designers can use such a framework to study the low‐level impact sensitivity of munitions in a computationally efficient manner. Results of the simulation using the hybrid model suggest that copper anvil undergoes plastic deformation which absorbs a significant portion of the impact energy reducing the energy dissipated within the EM and suppressing ignition.

Effect of RDX powders on detonation characteristics of emulsion explosives

ABSTRACTTo obtain an explosive suitable for the explosive welding of foils and produce a new way to reuse demilitarized explosives, RDX powders and high amounts of hollow glass microballoons (GMs) were introduced into an emulsion matrix to reduce detonation velocity and critical thickness. The effect of different percentages of RDX on the detonation performance of the mixtures was systematically investigated. The results showed that the critical thickness decreased significantly with increasing RDX contents, and the detonation velocity at the critical thickness was almost unchanged for the different RDX contents. Thus, the as-created mixtures were suitable for the explosive welding of foils due to their low detonation velocities and low critical thicknesses. The brisance test results indicated that the brisance of the composite explosives increased with increasing RDX contents, and this trend was more remarkable at low RDX contents. All the energy output parameters of the underwater explosions also increased with increasing RDX contents.

Synthesis, Crystal Structure, and Properties of Energetic Complexes Constructed from Transition Metal Cations (Fe, Co, Cu, and Pb) and BTO2−

Four transition metal energetic complexes with 5,5′‐bistetrazole‐1,1′‐diolatedehydrate (BTO) have been synthesized and structurally characterized by FT‐IR spectroscopy, elemental analysis, and single X‐ray diffraction. The thermal decomposition processes of the complexes and BTO were studied by means of the TG‐TDA technologies. The compatibility of the four complexes with RDX, HMX, NC, and Al powder was also investigated. Sensitivity tests reveal that the complexes are more insensitive to mechanical stimuli than RDX.

Thermodynamic Simulation of the RDX–Aluminum Interface Using ReaxFF Molecular Dynamics

We use reactive molecular dynamics (RMD) simulations to study the interface between cyclotrimethylene trinitramine (RDX) and aluminum (Al) with different oxide layers to elucidate the effect of nanosized Al on thermal decomposition of RDX. A published ReaxFF force field for C/H/N/O elements was retrained to incorporate Al interactions and then used in RMD simulations to characterize compound energetic materials. We find that the predicted adsorption energies for RDX on the Al(111) surface and the apparent activation energies of RDX and RDX/Al are in agreement with ab initio calculations. The Al(111) surface-assisted decomposition of RDX occurs spontaneously without potential barriers, but the decomposition rate becomes slow when compared with that for RDX powder. We also find that the Al(111) surface with an oxide layer (Al oxide) slightly increases the potential barriers for decomposition of RDX molecules, while α-Al2O3(0001) retards thermal decomposition of RDX, due to the changes in thermal decompositi...

Influence of Anvil Properties on RDX Thin Layer Ignition Behavior

AbstractWe report on a drop‐impact protocol that arrests sample radial flow to isolate how anvil properties influence ignition in a thin layer of RDX powder. To eliminate sliding friction as a probable heating mechanism, flow arrestment was provided by a waxed weighing paper that shielded the RDX layer from direct contact with the impact surfaces. RDX reaction sensitivity under bare and shielded conditions for the standard O1 hardened steel anvil was compared with that for two deformable anvil types: 1018 steel and C110 copper. Profilometer measurements of anvil deformation and paper impressions quantified anvil plastic work and final radial flow displacement. Post‐test particle analyses correlated particle size distribution to ignition results. Experiments indicated that the impact energy absorbed by the anvils was varied and inhibited ignition accordingly. For the standard anvil, ignition was not inhibited under flow arrestment, suggesting that significant radial sliding or flow is not essential for thin layer ignition.

The Mechanical Properties of Minimally Processed RDX

We report for the first time the mechanical properties of RDX crystals in a conventionally processed, sub-millimeter form that have had no additional mechanical processing. Nanoindentation of RDX powders was used to measure the elastic modulus (19.1±1.9 GPa), hardness (0.741±0.098 GPa), and yield point (onset of plastic deformation) on the as-grown faces of seven different RDX crystals, selected to provide random orientations. Properties within each crystal showed narrow distributions, while the range of properties across all crystals is indicative of testing a variety of orientations. The elastic modulus and hardness are within the range of other published reports on bulk and mechanically polished RDX. The distribution in yield point behavior, with the onset of plasticity occurring between 0.1 and 0.7 GPa, indicates that powders of RDX likely contain a significant number of dislocation sources in the as-processed condition, suggesting that deformation sources are prevalent in the energetic component of plastic bonded explosives prior to incorporating into pressed forms.

Indicating Inconsistency of Desensitizing High Explosives against Impact through Recrystallization at the Nanoscale

ABSTRACTMicroscaled 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) is recrystallized by the spray flash evaporation technique to obtain nanoscaled RDX powder. Recrystallization is tracked by diverse methods, including atomic force microscopy and X-ray diffraction. Reduced sensitivity to friction and electrostatic discharge as a consequence of less internal defects within the RDX nanocrystals makes recrystallized material more favorable against unwanted ignition. Increased sensitivity to impact of the nanomaterials is detected and desensitization is discussed in detail with regard to hot-spot theory and potential influencing variables. Surface engineering of nano-RDX by the above-mentioned spray process shows desensitization against stimuli from impact.

Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry

The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets. The TGA was calibrated using ferrocene as a standard material of well-characterized sublimation rates and vapor pressures to determine the vapor pressures of TNT, PETN, and RDX. The determined sublimation rates and vapor pressures were used to indirectly determine the diffusion coefficients of TNT, PETN, and RDX for the first time. A linear log–log dependence of the diffusion coefficients on temperature is observed for the three materials. The diffusion coefficients of TNT, PETN, and RDX at 273K were determined to be 5.76×10−6m2/sec, 4.94×10−6m2/s, and 5.89×10−6m2/s, respectively. Values are in excellent agreement with the theoretical values in literature.

The Critical Energy of Direct Initiation in Liquid Fuel‐Air and Liquid Fuel‐RDX Powder‐Air Mixtures in a Vertical Detonation Tube

AbstractMultiphase cloud detonation is an important but complex process, which has not been fully understood yet. Direct experimental data about the critical initiation energy (CIE) and pressure/velocity revolution of high explosive powder‐based multiphase cloud detonation is not available in the literature. In this paper, propylene oxide (PO), petroleum ether (PE), isopropyl nitrate (IPN), and a mixture of PE/IPN were individually dispersed to form a cloud in a 200 mm×5400 mm vertical detonation tube. Subsequently, this cloud was directly ignited by a high explosive. The critical initiation energy of various mist/air mixtures was measured by the up and down method. Meanwhile, the pressure history was recorded by six sensors along the detonation tube. RDX powder was added to the system and sprayed simultaneously with the liquid fuel to form a three‐phase gas‐liquid‐solid explosive cloud. The detonation pressure and velocity of all three‐phase cases significantly increased while the corresponding critical initiation energy decreased compared to the liquid‐air analogs. The CIE data were found to have a “U”‐shaped curve relationship to the fuel‐air ratio in two‐ and three‐phase systems, the minimum is always on the fuel‐rich side.

Calculation of the detonation velocity of porous water-containing RDX-based charges

A nomographic method for predicting the detonation velocity of a porous explosive mixture prepared from RDX powder and water is proposed. It is shown that, in contrast to the existing calculation methods for predicting the detonation velocity, the use of the proposed nomogram greatly simplifies the procedure and requires knowledge of only two parameters: the mass fraction of RDX and the density of the mixture in the charge. At the same time, the nomogram is a coordinate system that enables to place and to compare on one field experimental data obtained at different parameters of the charge. It is shown that RDX powder-water hand-prepared charges can have a detonation velocity of 6–8 km/s. The detonation velocity of cylindrical water-containing charges 10–36 mm in diameter and 120–1000 mm in length with RDX mass fractions of 0.6–1.0 is measured.

Experimental investigations of the controlled explosive synthesis of ultrafine Al2O3

The relation between the parameters of mixed explosives [combinations of Al(NO3)3·9H2O powder, RDX powder, and/or polyethylene foaming particles] and the phase and dimension of ultrafine Al2O3 is studied in this paper. Experimental results indicate that mixed explosives with a high density of 1.8 g/cm3 are adapted to prepare high-temperature α-Al2O3. Ultrafine (α + γ)-Al2O3 with α-phase dominance is synthesized by the detonation of charges with a medium-high density of 1.3 g/cm3. Explosives with a medium-low density of 0.8 g/cm3 synthesize low-temperature pure λ-Al2O3.

Synthesis, crystal structure and properties of energetic complexes constructed from transition metal cations (Fe and Co) and ANPyO

Two transition metal energetic complexes with ligand 2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO) have been synthesized and structurally characterized by FT-IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. The thermal decomposition processes and the kinetic parameters of the two complexes were studied by means of the TG-DTG and DSC technologies. The compatibility of the two complexes with RDX (1,3,5-trinitrohexahydro-1,3,5-triazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), NC and Al powder was also investigated. DSC measurements show that both complexes have significant catalytic effects on the thermal decomposition of ammonium perchlorate. Sensitivity tests reveal that the two complexes are more insensitive to mechanical stimuli than ANPyO.

Preparation and characterization of cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) powder: Comparison of microscopy, dynamic light scattering and field-flow fractionation for size characterization

Abstract RDX powder was prepared using a supercritical anti-solvent (SAS) recrystallization. Then the physicochemical properties of the RDX powder were analyzed by using differential scanning calorimetry (DSC), electrophoretic light scattering (ELS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The size distribution of the RDX powder was studied by dynamic light scattering (DLS) and optical microscopy (OM). Asymmetrical flow field-flow fractionation (AsFlFFF) was tested for determination of size distribution. Results from FFF were compared with those from DLS and OM, and then the merits and limitations of the sizing techniques were discussed. It was found that DLS is not suitable for the size analysis of samples having broad size distributions, such as the RDX powder prepared in this work. The mean sizes of the RDX powder obtained by OM and FFF were in reasonable agreement. For FFF analysis, combination of FL-70, a surfactant, with regenerated cellulose (RC) membrane was found to provide the best performance with good resolution and minimized particle-membrane interaction, resulting in reliable size distribution. The FFF technique showed higher reproducibility in measuring the particle size than OM or DLS with relative standard deviation of 6%. FFF is a useful tool for size-based separation and size characterization of the RDX powder with a particle size distribution from about 1 μm to 25 μm.

Explosive Mixtures for Explosive Welding of Thin Foils: Part 2. RDX-Baking Soda Mixtures

Explosive mixtures of RDX powder and baking soda have been investigated. It was found that the size of the RDX particles had crucial influence on the detonation properties of such explosives. The suggested mix of explosives can be recommended for use in explosive welding and some other applications.

Production and Sensitivity Evaluation of Nanocrystalline RDX‐based Explosive Compositions

AbstractThe initiation sensitivity of cyclotrimethylenetrinitramine (RDX) was investigated as a function of crystal size. For this study, RDX powders with mean crystal sizes of ca. 200 and 500 nm were prepared by rapid expansion of supercritical solutions (RESS) with carbon dioxide as the solvent. Initiation sensitivity testing to impact, sustained shock, and electrostatic discharge stimuli was performed on uncoated as well as wax‐coated specimens. The test data revealed that in a direct comparison to coarser grades the nanocrystalline RDX‐based samples were substantially less sensitive to shock and impact stimuli. Furthermore, the 500 nm RDX‐based specimens exhibited the lowest sensitivity values, an indication that minima in shock and impact sensitivities with respect to crystal size exist.

English

Two kinds of RDX samples, with broad and narrow particle size distribution, have been fabricated by wet riddling and solvent/non-solvent methods, respectively. By controlling the technical condition, the RDX powders with different particle sizes were obtained for each sample. All samples were characterised by laser granularity measurement and scanning electron microscope (SEM). Using mechanical sensitivity tests, slow cook-off test and differential scanning calorimetry (DSC), the mechanical safety and thermal stability of RDX samples, depending on the particle sizes and size distribution, were studied. Results indicated that, for each kind of RDX particles, the mechanical sensitivity and thermal stability of samples changed according to the particle size. However, although two samples had almost the same average particle size, their safety changed when two particle size distributions differed. Concretely, the mechanical sensitivity of RDX reduced and their thermal stability increased gradually along with the decreasing of particle size. Meanwhile, RDX with broad size distribution had higher mechanical sensitivity and thermal stability than samples with narrow size distribution.Defence Science Journal, 2009, 59(1), pp.37-42, DOI:http://dx.doi.org/10.14429/dsj.59.1482

Effects of copper micro-particles on the detonation characteristics of RDX powder

The effects of copper micro-particles on the detonation characteristics of RDX powder were investigated in a horizontal shock tube with internal dimensions of 100 mm diameter and 4 m length using an instantaneous spectrum detection apparatus. The emergence time and emission spectral intensity of the main products such as NO2, H, C2, O, CO, CH2O, CO2 and H2O were observed by a TDS5054 oscilloscope. With or without the addition of copper micro-particles into RDX, NO2 appears first in every experiment, which is in agreement with theoretical results. However, the addition of copper micro-particles to RDX can shorten the emergence time by 7–18%; it can also increase the peak blast pressure by about 133%. In addition, O2, H2O and CH2O in various quantities were introduced into this experiment, respectively, which indicate that O2 can obviously affect the results that may shorten the emergence time of NO2 by 31% and increase the peak blast pressure by 167%.