RDX Samples Research Articles

TNT and RDX extraction from B explosives**

AbstractThe recycling of discarded military bombs holds significant importance in improving energy efficiency within the military field. In this study, we employed first‐principles calculations (DFT) to compute the affinity of toluene, acetone, and dimethyl sulfoxide (DMSO) towards TNT and RDX, highlighting the solubility differences that enable their effective separation. Furthermore, through recovery and separation experiments, we successfully obtained TNT and RDX samples, which were then characterized using gas chromatography‐mass spectrometry (GC‐MS) and scanning electron microscopy (SEM) to experimentally validate the results obtained from molecular simulation experiments. The results revealed that using toluene for the extraction and recovery of TNT and RDX from waste B explosives yielded the highest recovery efficiency and component purity. SEM analysis showed that TNT extracted with toluene exhibited a regular layered surface, while RDX particles demonstrated a more uniform distribution. This study provides a theoretical basis for the separation and recovery of TNT and RDX from waste B explosives using extraction methods, from the perspective of molecular simulation.

Study of terahertz reflection spectra of optically thin RDX samples by terahertz imaging with spectral resolution

The THz reflection spectra of optically thin hexogen (RDX) samples were studied by terahertz imaging with spectral resolution. A photoconductive antenna excited by femtosecond laser radiation was used as a source of broadband THz radiation. The presence of a Fourier spectrometer (as well as band-pass THz filters) and a microbolometric THz video camera in the experimental setup made it possible to use the terahertz imaging method to study reflection spectra taking into account scattering in the range of 0.6 to 1 THz. The influence of the optical characteristics of the substrate on the THz reflection spectra was studied. In particular, the conditions for observing the effect of anomalous dispersion for RDX samples with different dispersion in the frequency region of the RDX absorption band 0.8 THz were studied. The obtained results demonstrate the application of the method of terahertz imaging with spectral resolution based on THz video camera for the identification of explosives with concentrations 0.75 to 50 mg / cm2 on various surfaces.

A Study on the Effect of Initial Temperature on Combustion Characteristics of RDX Based on the Optical Diagnosis Methods

The purpose of this work is to investigate the effect of different initial temperatures on the combustion characteristics of RDX materials. In the experiments, the electric heating plate below the RDX samples was controlled so that the initial temperatures were set to be 298, 323, 373, 423, and 473 K (below the material melting point), respectively. Three optical diagnostic methods were employed to capture the ignition process, flame thermal radiation, and NO distribution in the flame at different conditions. The results show that the increase in initial temperature can improve the reaction rate, shorten the ignition delay time, and increase the flame combustion intensity and speed, because of the earlier evaporation and pyrolysis process in the RDX samples. Increasing the initial temperature also enhances the thermal effect of the flame, which is related to the generation and consumption of NO to a certain extent.

Detection of aging in the common explosive RDX using terahertz time-domain spectroscopy

A method to detect the aging in cyclotrimethylene-trinitramine (RDX), using terahertz (THz) waves, is reported in this paper. The absorption spectra of RDX are analyzed, and any changes of the characteristic absorption peaks (before and after aged treatment of RDX in laboratory) are compared. When RDX samples undergo aging, the characteristic absorption peaks (at 1.02 THz, 1.36 THz, 1.58 THz, and 2.37 THz) disappear, which corresponds to the fracture of N- N O 2 bonds in RDX molecules. These results show that THz time-domain spectroscopy technology may be used not only for analysis but also for detection of aging in RDX and similar materials.

RDX remote Raman detection on NATO SET-237 samples

Ultraviolet Raman spectroscopy measurements have been taken at DLR in Lampoldshausen to detect NATO SET-237 standard samples of RDX. The main goal was to quantify the minimum requirements for an unambiguous identification in remote detection (60 cm distance) with a commercial Czerny–Turner spectrometer coupled with a CCD camera. Well-defined distribution of explosives on surfaces was tested as standardized samples. Therefore, Raman spectra of RDX have been acquired for different sample concentrations (50, 250 and 1000 μg/cm2, respectively) and under several laser energies (1.5, 3.0 and 5.0 mJ/pulse, respectively) at 355 nm excitation wavelength. The lowest possible reproducible surface concentration (50 µg/cm2) was detected with excitation energy of 3 mJ/pulse in the described configuration.

Molecular Dynamics Simulation of the Influence of RDX Internal Defects on Sensitivity

The internal defect is an important factor that could influence the energy and safety properties of energetic materials. RDX samples of two qualities were characterized and simulated to reveal the influence of different defects on sensitivity. The internal defects were characterized with optical microscopy, Raman spectroscopy and microfocus X-ray computed tomography technology. The results show that high-density RDX has fewer defects and a more uniform distribution. Based on the characterization results, defect models with different defect rates and distribution were established. The simulation results show that the models with fewer internal defects lead to shorter N-NO2 maximum bond lengths and greater cohesive energy density (CED). The maximum bond length and CED can be used as the criterion for the relative sensitivity of RDX, and therefore defect models doped with different solvents are established. The results show that the models doped with propylene carbonate and acetone lead to higher sensitivity. This may help to select the solvent to prepare low-sensitivity RDX. The results reported in this paper are aiming at the development of a more convenient and low-cost method for studying the influence of internal defects on the sensitivity of energetic materials.

Ignition and Combustion Developments of Granular Explosive (RDX/HMX) in Response to Mild‐Impact Loading

AbstractThe experimental analyses of ignition and burning responses of mild‐impacted granular explosive, namely, cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX), were performed based on an optimized drop‐weight system equipped with a High‐Speed Camera (HSC). It has been found that jetting phenomena observed by HSC is the result of the energy released by gaseous products, which push the pulverized or melted explosives to splash radially. Jetting is the only and the most obvious difference between reactive and inert particles prior to combustion so that it can be regarded as the sign of ignition more accurately than other ways. For RDX sample, the molten phase plays an important role in the hot‐spots formation. After a piece of waxed paper is put on the glass anvil, the jetting of molten‐phase RDX will be limited due to the high‐roughness of waxed paper. Moreover, ignition growth to burning probability of RDX particles is increased compared with the non‐waxed paper case. Radial deformation velocity, jetting velocity, and flame propagation velocity have been estimated via image processing, making it possible to quantify the violence of mechanical deformation and chemical reaction.

Optical absorption in polycrystalline PETN, RDX, HMX, CL-20 and HNS and its possible effect on exploding bridgewire detonator function

ABSTRACT Exploding bridgewire (EBW) detonators work by bursting a thin conducting wire as a result of a high voltage discharge. This process is known to produce a strong UV emission. The roles of optical absorption, photochemistry, shock sensitivity, and impact sensitivity are assessed with respect to the relative roles each plays in the operation of an EBW detonator. The optical absorptivity and penetration depth have been measured using dilute polycrystalline samples of PETN, RDX, HMX, CL-20 and HNS in KBr between 190 and 1100 nm. The results show strong absorption at UV wavelengths with a gradual decline at longer ones. It is found that while strong UV absorption appears to be necessary, it is not sufficient to make an effective EBW detonator.

Infrared Reflectance Spectroscopic Evaluation of Inkjet Printed Standards of Cyclotrimethylenetrinitramine (RDX) on Aluminum Substrates.

The Department of Defense (DOD) and first responder communities are evaluating and developing optical systems for the detection and identification of explosives and components used for assembling homemade explosives (HMEs). Emerging detection technologies must be evaluated with authentic hazard material concentrations to ensure their accurate and reliable use in the field. In this work, infrared (IR) reflectance spectra over the spectral rage of 1000-1700 cm-1 were collected for different concentrations of inkjet-printed RDX (cyclotrimethylenetrinitramine) samples deposited onto aluminum substrates. A plot of the integrated area of both the symmetric and asymmetric NO2 vibrational bands for RDX on aluminum exhibited good linearity over the concentration range 20-500 µg/cm2. Detection limits for RDX on an aluminum surface were calculated to be 10.7 µg/cm2 for the symmetric NO2 vibrational band and 1.4 µg/cm2 for the asymmetric NO2 vibrational band. Evaluation of the NO2 vibrational band areas at different locations of the RDX array demonstrated that the samples exhibited good homogeneity across the surface. The concentration of an unknown sample of RDX on aluminum was determined using the fitted equations; results showed good agreement between the calculated and actual RDX surface concentration. The lot-to-lot variation of RDX on the aluminum surface was compared using the long wavelength infrared (LWIR) spectral band areas for two different lots of standards printed at the same RDX surface concentration. Results showed excellent lot-to-lot agreement indicating good reproducibility of the standards for RDX.

Trace detection of explosive and their derivatives in stand-off mode using time gated Raman spectroscopy

Trace detection is utmost important for detection of concealed explosive materials in form of IEDs. Surfaces of suspicious objects may be scanned for contamination of explosives. Sensitivity and selectivity are two main concerns in field of explosive detection. Raman spectroscopy provides remarkable selectivity. Time-gated Raman spectroscopy also has potential of providing sensitivity for trace detection. In present study, time-gated Raman spectroscopy investigated for detection of ppm level concentration of explosives. To achieve better sensitivity, various parameters of the experimental set-up like gain of intensifier, number of pulse accumulated and pulse energy of laser were optimised. The trend of change in intensity of Raman scattering (background subtracted) was observed by varying values of these above mentioned parameters. Followed by optimization of these parameters for better sensitivity, Raman spectra of RDX samples at lower concentrations (prepared by mixing RDX with KBr) were recorded. The corrected intensity increased in linear fashion with increase in gain of intensifier, number of pulses accumulated and pulse energy. After that, Raman spectra of RDX were recorded from a stand-off distance of 5m in backscattered mode with concentrations down to 100ppm.

Burning Characteristics of Microcellular Combustible Objects Fabricated by a Confined Foaming Process

AbstractMicrocellular combustible objects for application of combustible case ammunition and caseless ammunition were fabricated by a confined pressure quenching foaming process using supercritical CO2 as foaming agent. The experimental results showed that the force constant (f) of objects obviously increased with an increasing RDX content and that the force constant of formulation with 55 % RDX is comparable to that of traditional felted case. Pressure histories, dp/dt‐t, and dynamic vivacity curves were investigated and compared by closed vessel tests. The influencing factors such as RDX content, expansion ratio, foaming temperature, sample size, and loading density were analysed. The results revealed that RDX content and expansion ratio significantly affected the burning properties, whereas the foaming temperature did not have obvious influence. Moreover, the burning behavior also changed with sample size and loading density.

A Successive and Scalable Process for Preparing Spherical Submicrometer-Sized RDX by the SEDS Process

The preparation spherical and submicrometer-sized cyclotrimethylene-trinitramine (RDX) is described through the process of solution-enhanced dispersion by supercritical fluids (SEDS). Because SEDS is a successive and scalable process, about 40.5 g RDX particles can be obtained within 70 min and the total yield is about 90.0% under optimized conditions. Submicrometer-sized RDX and original samples were characterized and confirmed by different analysis methods. The results revealed that submicrometer-sized RDX particles are spherical with a mean particle size of 767.7 nm, have high purity, show no crystal structure change, and decompose easily. Mechanical sensitivity tests of submicrometer-size RDX were decreased in comparison to the original RDX.

Spectrochemical properties of some explosives in the vapor state

The FTIR spectra of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and pentaerythritol tetranitrate (PETN) in the vapor phase over wide frequency (3500–500 cm−1) and temperature ranges (293–383 K) is experimentally studied and the assignment of the observed vibrational bands is performed. To clarify the nature of the physicochemical processes that occur during the heating and evaporation of RDX and PETN and to detect and identify their characteristic components, the mass spectra and sub-THz spectra of these explosives are studied. To obtain spectroscopic information, special experimental techniques for recording of IR, sub-THz, and mass spectra of vapors of explosives and for preparation of high-purity RDX and PETN samples (with a main substance content of >99.7%) are developed based on modern methods of synthesis and purification.

Kinetic investigation on thermal decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) nanoparticles

This is a study of the thermal decomposition of hexahydro-1,3,5-trinitro-1,3,5-triazine or cyclotrimethylenetrinitramine (RDX) nanoparticles by simultaneous thermo-gravimetry differential thermal analysis (TGA/DTA) and differential scanning calorimetry (DSC) under nonisothermal conditions, at various heating rates from 5 to 20°Cmin−1. The influence of particle size on the thermal decomposition was verified. The activation energy for the decomposition of each sample was calculated using the peak temperature shift method, proposed by Kissinger and Ozawa. A significant variation in varying particle observed the results size of RDX. The results showed that, as the particle size of RDX is increased the thermal decomposition temperature of RDX and its decomposition activation energy are enhanced. The values of activation energy obtained by the Kissinger and Ozawa methods for RDX samples with various particle sizes show that the activation energy for micron sized RDX is 1.5 times higher than that for nano-RDX.The values of ΔS#, ΔH# and ΔG# of decomposition reaction for each particle size were also computed. Base on the kinetic data, the relative sensitivity of RDX samples was found in the order: 180nm RDX>250nm RDX>300nm RDX>50μm RDX.

Non-equilibrium molecular dynamics simulation study of heat transport in hexahydro-1,3,5-trinitro- s-triazine (RDX)

The direct estimation of thermal conductivity in solids using the constant flux non-equilibrium molecular dynamics (NEMD) simulation method has proven to be difficult with significant differences still existing for various, even simple, systems. The application of NEMD to study the thermal transport in molecular solids was rarely attempted. We report the first application of NEMD based on the Ikeshoji and Hafskjold (NEMD-IH) scheme to study the thermal conductivity of crystalline hexahydro-1,3,5-trinitro- s-triazine (RDX), an important energetic material, at temperatures T = 230, 275, and 300 K for different sample sizes and different crystallographic directions. We found that the size effects arising from a finite distance between sources of heat in the NEMD-IH simulation show a well-defined linear dependence on the inverse of the sample length within the errors of simulation. The thermal conductivity exhibits anisotropy with the largest value found along the [0 0 1] crystallographic direction and the smallest value along the [0 1 0] direction. The extrapolated value of the directionally averaged thermal conductivity coefficient κ ¯ to the sample of infinite length (e.g. 0.355 W/Km at T = 300 K ) is higher, but still in reasonable agreement with existing experimental data for powdered samples. The NEMD-IH heat transport properties were reproduced in a broad range of values of heat flux and sizes of heat source regions. Surprisingly, the thermal conductivity coefficient at T = 275 K is found to be higher by about 13% than at T = 300 K and 230 K, which may suggest a location of the temperature maximum above 230 K. A similar location of the low temperature peak was reported from experiments on powdered samples of RDX. Through the use of additional calculations based on the Green–Kubo approach, we discuss the possible origins of such a behavior in the NEMD-IH approach.

Trace detection and discrimination of explosives using electrochemical potentiometric gas sensors

In this article, selective and sensitive detection of trace amounts of pentaerythritol tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) is demonstrated. The screening system is based on a sampling/concentrator front end and electrochemical potentiometric gas sensors as the detector. Preferential hydrocarbon and nitrogen oxide(s) mixed potential sensors based on lanthanum strontium chromite and Pt electrodes with yttria stabilized zirconia (YSZ) solid electrolyte were used to capture the signature of the explosives. Quantitative measurements based on hydrocarbon and nitrogen oxide sensor responses indicated that the detector sensitivity scaled proportionally with the mass of the explosives (1–3 μg). Moreover, the results showed that PETN, TNT, and RDX samples could be discriminated from each other by calculating the ratio of nitrogen oxides to hydrocarbon integrated area under the peak. Further, the use of front-end technology to collect and concentrate the high explosive (HE) vapors make intrinsically low vapor pressure of the HE less of an obstacle for detection while ensuring higher sensitivity levels. In addition, the ability to use multiple sensors each tuned to basic chemical structures (e.g., nitro, amino, peroxide, and hydrocarbon groups) in HE materials will permit the construction of low-cost detector systems for screening a wide spectrum of explosives with lower false positives than present-day technologies.

Neutron scattering study of internal void structure in RDX

We present the first small and ultrasmall angle neutron scattering (SANS/USANS) measurements of the internal void morphology of the high explosive RDX on length scales from 10 Å to 20 μm. Measurements were taken on a range of RDX samples with similar densities and particle size distributions but which have significantly different sensitivities to shock initiation as measured by large-scale gap tests of the samples when formulated in standard polymer blends. Scattering measurements were performed using a contrast match technique to eliminate all features apart from internal void structures. The dominant feature in all samples is a surface fractal scattering that extends from ∼50 nm to above 20 μm, with no observable upper bound for the fractal correlation length. These features are interpreted in terms of scattering from rough surfaces of interior air-filled voids with fractal dimensionality between 2.4 and 2.9. The fractal pattern is proposed to arise from complex growth patterns on void surfaces as internal solvent diffuses out of the crystallites. No evidence of distinct nanometer-scale voids is observed in any of our RDX samples. The neutron scattering invariant calculated over the measured SANS and USANS range, a gauge of the volume fraction of voids smaller than 20 μm, tracks well with sensitivity testing of the materials.

Bioassays for bomb-makers: proof of concept

Clandestine bomb-makers are exposed to significant amounts of explosives and allied materials. As with any ingested xenobiotic substance, these compounds are subject to biotransformation. As such, the potential exists that characteristic suites of biomarkers may be produced and deposited in matrices that can be exploited for forensic and investigative purposes. However, before such assays can be developed, foundational data must be gathered regarding the toxicokinetics, fate, and transport of the resulting biomarkers within the body and in matrices such as urine, hair, nails, sweat, feces, and saliva. This report presents an in vitro method for simulation of human metabolic transformations using human liver microsomes and an assay applicable to representative nitro-explosives. Control and metabolized samples of TNT, RDX, HMX, and tetryl were analyzed using high-performance liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS) and biomarkers identified for each. The challenges associated with this method arise from solubility issues and limitations imposed by instrumentation, specifically, modes of ionization.

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

Compound-Specific Isotope Analysis of RDX and Stable Isotope Fractionation during Aerobic and Anaerobic Biodegradation

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production sites. Here, we report on the use of compound-specific isotope analysis of RDX to obtain delta(15)N and delta(18)O enrichment factors during biodegradation in batch cultures. A new preparation method has been developed based on RDX purification using thin-layer chromatography. RDX is then subjected to an elemental analyzer coupled with an isotope-ratio mass spectrometer (EA-IRMS). The precision of the method shows standard deviations of 0.13% per hundred and 1.18% per hundred for delta(15)N and delta(18)O, respectively, whereas the accuracy of the method has been checked routinely, adhering to external standards. The method was applied to RDX samples subjected to biodegradation under aerobic or anaerobic conditions. Enrichment factors under aerobic conditions were -2.1% per hundred and -1.7% per hundred for delta(15)N and delta(18)O, respectively, and under anaerobic conditions, -5.0% per hundred and -5.3% per hundred for delta(15)N and delta(18)O, respectively. The results of this study provide a tool for monitoring natural attenuation of RDX in a contaminated environment.