Nairmen Mina

Transport of explosives I: TNT in soil and its equilibrium vapor

Landmine detection is an important task for military operations and for humanitarian demining. Conventional methods for landmine detection involve measurements of physical properties. Several of these methods fail on the detection of modern mines with plastic enclosures. Methods based on the detection signature explosives chemicals such as TNT and DNT are specific to landmines and explosive devices. However, such methods involve the measurements of the vapor trace, which can be deceiving of the actual mine location because of the complex transport phenomena that occur in the soil neighboring the buried landmine. We report on the results of the study of the explosives subject to similar environmental conditions as the actual mines. Soil samples containing TNT were used to study the effects of aging, temperature and moisture under controlled conditions. The soil used in the investigation was Ottawa sand. A JEOL GCMate II gas chromatograph ñ mass spectrometer coupled to a Tunable Electron Energy Monochromator (TEEM-GC/MS) was used to develop the method of analysis of explosives under enhanced detection conditions. Simultaneously, a GC with micro cell 63Ni, Electron Capture Detector (μECD) was used for analysis of TNT in sand. Both techniques were coupled with Solid-Phase Micro Extraction (SPME) methodology to collect TNT doped sand samples. The experiments were done in both, headspace and immersion modes of SPME for sampling of explosives. In the headspace experiments it was possible to detect appreciable TNT vapors as early as 1 hour after of preparing the samples, even at room temperature (20 °C). In the immersion experiments, I-SPME technique allowed for the detection of concentrations as low as 0.010 mg of explosive per kilogram of soil.

Nucleation and crystalization studies: a vibrational-spectroscopy investigation of 2,4,6-TNT

2,4,6-Trinitrotoluene, commonly known as TNT, is an explosive used in military shells, bombs, landmines, grenades, demolition operations, and underwater blasting. It is produced in the United States only at military facilities. Accidental releases of TNT and residues in battle fields have contaminated groundwater, soil, and sand at numerous sites around the world. TNT exists in two physical forms at room temperature: droplets and crystals. The spectroscopic information conveyed depends on its physical form and the substrate on which it is deposited. Vibrational spectroscopy is a powerful tool that can be used to characterize TNT in its diverse forms. Crystallization of TNT from different solvents (acetonitrile, methanol, and water) was carried out to subsequently measure the vibrational spectra. The important nitroaromatic compound exhibits a series of unique characteristic bands that allow its detection and spectroscopic characterization. The spectroscopic signatures of neat TNT samples were determined with Raman Microspectroscopy and Fourier Transform Infrared (FTIR) Microscopy. The Raman spectra of neat TNT are dominated by strong bands at about 1365 and 2956 cm-1. The intensity and even the presence of these bands are found to be remarkably dependent on TNT form and source.

Effect of water and common salts on the vibrational spectra of high energy cyclic organic peroxides

Cyclic organic peroxides are sensitive to the presence of water and other contaminants that can deactivate the substance or make it less sensitive to chock, spark or other detonating mechanism. In the case of radiation such as laser action the opposite seems to happen, making the peroxides more sensitive to laser breakdown and local burning. In recent studies, TATP has been induced to sublimate faster during Raman analysis when it had contaminants or water, however, some studies have shown that TATP does not reacts when it is wet. This study is focused on determining if the presence of water and other contaminants affects peroxide stability and the detection by current technologies, such as IMS and vibrational spectroscopy. During the study, TATP and HMTD have been synthesized by different methods using certified chemicals and common household products. The research also focused on the effect of metal salts in the syntheses and the effect of temperature in the composition of the products. Differences in the location, shape, relative intensity, and in some cases appearance of new bands possibly due to Redox and complex formation reactions were evident. Bands corresponding to ν(O-O), ν(C-O), δ(CH3-C) and δ(C-O) were located and assigned for Raman and IR spectroscopies.

Spectroscopic signatures of PETN: Part II. Detection in clay

Infrared Spectroscopy is a well established tool for standoff detection of chemical agents in military applications. Vibrational IR spectroscopic analysis can also be used in Chemical Point Detection mode and to the arena of explosives identification and detection when energetic compounds are in contact with soil. PETN is an important nitroaliphatic explosive for military applications. Due to its intrinsic explosive power, it can be used in laminar form or mixed with RDX to manufacture Semtex plastic explosive and in the fabrication of Improvised Explosive Devices (IEDs). This investigation focused on the study of spectroscopic signatures of PETN in contact with soil. For this study, clay was mixed in different proportions with PETN. Detection of the vibrational signatures of PETN constitutes the central part of the investigation. The mixtures were submitted to the effect of water, acid and alkaline solutions, heat and deep UV light (234 nm) in order to establish the effect on these environmental parameters on the vibrational signatures of the explosive in the mixtures. The results reveal that the characteristic bands of PETN are highly persisted, degraded only by extreme conditions of UV radiation and exposure to high temperature for prolonged time. These results could be used in the development of sensitive sensors for detection of landmines, and improvised explosives devices (IDEs).

Density-functional-theory calculations of TNT and its interaction with siloxane sites of clay minerals

2,4,6-trinitrotoluene (TNT) is the most used explosive as main charge in landmines. There have been found contamination of soil and groundwater with munitions residues of TNT due to buried landmines. We are investigating the molecular structure, vibration behavior and the binding energy of TNT with the siloxane surface site of clay minerals in order to determine the spectroscopic signature of TNT in soil. Two different molecular symmetry structures were found with density functional theory (DFT) B3LYP method with 6-31G, 6-31G*, 6-311G, 6-311G*, and 6-311+G** basis sets from the Gaussian 98 systems of programs. Different deformations of the phenyl ring and distortions of the nitro and methyl groups with the ring were observed. In both structures, C1 and Cs, the nitro groups in positions 2 and 6 are out of plane with the phenyl ring due to steric interaction with the methyl group while the nitro group in position 4 is planar to the phenyl ring. The difference between the two structures is the internal rotation of the methyl group and 2, 6-nitro groups. Comparison of the calculated energies of the two structures in several basis sets reveals that the lowest-energy geometry for the TNT structure corresponds to Cs symmetry with B3LYP/6-311+G**. FTIR spectra of TNT are presented and assigned assisted by B3LYP/6-311+G** result. The lowest-energy molecular structure of TNT was interacted with the basal siloxane surface of clay minerals to determine the binding energy (Eb) between them. The binding energy was obtained by optimizing the vertical distance, the rotational and inclination angles between TNT and siloxane surface using the B3LYP hybrid functional with different basis sets.

Spectroscopic signatures of PETN in contact with sand particles

The detection of explosive materials is not only important as an issue in landmines but also for global security reasons, unexploded ordnance, and Improvised Explosive Devices detection. In such areas, explosives detection has played a central role in ensuring the safety of the lives of citizens in many countries. Raman Spectroscopy is a well established tool for vibrational spectroscopic analysis and can be applied to the field of explosives identification and detection. The analysis of PETN is important because it is used in laminar form or mixed with RDX to manufacture Semtex plastic explosive and in the fabrication of Improvised Explosive Devices (IEDs). Our investigation is focused on the study of spectroscopic signatures of PETN in contact with soil. Ottawa sand mixed in different proportions with PETN together with the study of the influence of pH, temperature, humidity, and UV light on the vibrational signatures of the mixtures constitute the core of the investigation. The results reveal that the characteristic bands of PETN are not significantly shifted but rather appear constant with respect of the ubiquitous band of sand (~463 cm-1). These results will make possible the development of highly sensitive sensors for detection of explosives materials and IDEs.

Effect of environmental conditions on the spectroscopic signature of DNT in sand

Landmines have been a part of war technology for many years. As a result of the continued and indiscriminate use in approximately 90 countries landmines pose a severe and ever growing problem and a daily risk. Raman Spectroscopy is capable of providing rich information about the molecular structure of the sample and pinpoint detection of many chemicals, both of organic and inorganic nature. The presence of landmines in soils can be detected by Raman Spectroscopy sensing in a Point Detection modality, using characteristic vibrational signals of each explosive present in landmines. Detection of 2,4-DNT in sand and studies on how the vibrational signatures of 2,4-DNT is modified by interacting with soil particles and environmental conditions is reported. Raman Microspectrometers equipped with 514 nm and 785 nm laser excitation lines were used. The work focused in how the spectroscopic signatures of DNT in contact with Ottawa Sand are affected by the presence of humidity, pH, temperature, UV light and reaction times. Samples of mixtures of sand/2,4-DNT were analyzed by Raman Spectroscopy at 10, 50 and 100% water content and temperatures in range of 40-80 °C. Mixtures were also analyzed at different pH: 4, 7 and 10 and under ultraviolet light at 254 nm. Raman spectra were taken as a function of time in an interval from 24 to 336 hours (two weeks). Characteristic signals of 2,4-DNT were analyzed in different ranges 100-3800 cm-1, 600-1200 cm-1, 300-1700 cm-1 and 2800-3500 cm-1. The effect of these variables was measured during 45 consecutive days. It was confirmed that the decrease of characteristic vibrational signatures of 2,4-DNT can be attributed to increase of the degradation of 2,4-DNT by the simulated environmental conditions. Spectroscopic characterization of degradation products, both in contact with sand as well as airborne is under way. These results will make possible the development of highly sensitive sensors for detection of explosives materials and correlated with their degradation products in landmines.

Theoretical studies of the molecular structures of dinitrotoluenes and their interactions with siloxane site surface of clays

Among the many different signature compounds emitted from a landmine in the vapor phase, 2,4-dinitrotoluene (2,4-DNT) is the most common nitroaromatic compound in terms of detecting buried landmines, although it is a byproduct in the synthesis of TNT. 2,4-DNT is used as an ingredient in mining explosives and also prevalent on the soil surface but is somewhat seasonally dependent. The B3LYP hybrid functional was used to obtain the lowest-energy structure of both 2,4 and 2,6-DNT. Increasing basis sets from the 3-21G up to the 6-31++G (d, p) are used to predict structural parameters, vibrational frequencies, IR intensities and Raman activities for the explosives molecules. The calculated energies show that the 2,4-dinitrotoluene isomer is more stable than 2,6-dinitrotoluene isomer due to the lesser levels of steric effects between the nitro groups and the methyl group. The optimized structures were interacted with the siloxane site of clay minerals, using the density functional level of theory and the basis sets used to optimize the geometry of the DNT molecules. The binding energy (Eb) between the optimized molecules and the basal siloxane site surface of clay minerals was calculated at distances in a range between 2.5 to 8.5 Å.

Raman and scanning electron microscopy measurements of RDX on glass substrates

Trace explosive detection is a major technological challenge. Spectroscopic characterization of explosive traces is a major step toward explosive detection strategies and sensor development. We report here on white light imaging measurements and Raman microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and energy dispersed X ray analysis (EDX) for the characterization RDX nanoparticles deposited on glass substrates surfaces. The RDX nanoparticles were prepared by exposure of glass substrate surfaces to an aerosol jet containing RDX. An average RDX particle size of 300 nm is determined from the SEM measurements. The spectroscopic signature of the RDX nanoparticles between 750 and 950 cm-1 is dominated by the ring breathing mode centered at about 877 cm-1. The smallest particle characterized with vibrational spectroscopy measurements are about 750 nm in size.

Improved detection of landmine components: using TEEM-GC-MS for detection of TNT and RDX in soil and other complex matrices

Nitrogen-rich compounds have a large cross section for resonance electron capture at very low incident electron energies. Although this fact has been known for a number of years, full benefit of this ubiquitous property of NOX compounds for explosives detection studies has not been fully implemented. Here we report detection of picogram to femtogram levels of TNT, 2,4-DNT and RDX in soil samples and other complex matrices. Toluene extracts as well as thermally desorbed GC-MS analyses were conducted using a JEOL GCmate II coupled to a Tunable-Energy Electron Monochromator (TEEM). Use of TEEM-GC/MS permitted rapid sweeping of electron energy and tuning of the electron monochromator and ion source while monitoring the electron capture resonance in real time. In addition, Solid-Phase Micro-Extraction (SPME) was used to selectively preconcentrate analytes prior conventional GC/MS analysis. The SPME protocol was able to screen explosives in spiked water, in concentrations below the reported detection limits. Standard solutions of TNT were prepared in the range of interest (0.5-10 ppm) and analyzed using a GC/MSD direct injection. Potential use of developed methodology in landmine environmental studies and sensors development will be discussed.