Fiber optics coupled-grazing angle probe Fourier transform infrared (FTIR) spectroscopy and infrared microspectroscopy have been used for characterization of the distribution and form of layers of some explosives deposited on stainless steel sheets. Among the explosives tested were trinitrobenzene, HMX and Tetryl. Various solvents were used to deposit the films on stainless steel slides. Isopropyl alcohol was the preferred solvent because it produced more homogeneous mass distributions of target explosives on the substrates. The film thickness, analyte distribution and the relation of thickness to infrared absorption/reflection response of these explosives were compared with those previously reported for TNT, 2,4-DNT and RDX. This comparison was used for described the general optical behavior of the explosives studied.
The use of liquid explosives by terrorists has raised the attention to the use of hazardous liquids as threats to people,
buildings and transportation systems. Hazardous liquids such as explosive mixtures, flammables or even chemical
warfare agents (CWA) can be concealed in common containers and pass security checks undetected. This work
presents three non invasive, non destructive detection approaches that can be used to characterize the content of
common liquid containers and detect if the liquid is the intended or a concealed hazardous liquid. Fiber optic
coupled Raman spectroscopy and Stand off Raman spectroscopy were used to inspect the content of glass and
plastic bottles and thermal conductivity was used to asses the liquid inside aluminum cans. Raman spectroscopy
experiments were performed at 532 nm, 488 nm and 785 nm excitation wavelengths. The hazardous liquids under
consideration included CWA simulant DMMP, hydrogen peroxide, acetone, cyclohexane, ethanol and nitric acid.
These techniques have potential use as a detector for hazardous liquids at a check point or to inspect suspicious
bottles from a distance.
This work was focused in the measurement of spectroscopic signatures of Chemical Warfare Agent Simulants (CWAS)
and degradation products of chemical agents using vibrational spectroscopy for the generation of spectroscopic libraries.
The chemicals studied were: DMMP, DIMP, 2-CEES, 2-BAET, 1,4-thioxane, thiodiglycol sulfoxide, dihexylamine,
cyclohexylamine, among others. Raman microscopy experiments were performed at different excitation wavelengths
that spanned from NIR at 1064 and 785 nm to the VIS at 532, 514.5 and 488 nm and even the deep ultraviolet region at
244 nm. For the compounds studied the optimum excitation lines were 488 nm and 532 nm with a laser power of 25
mW. Among the most prominent bands were at these incident wavelengths were located ca. 652 and 1444 cm-1. Fourier
Transform Infrared Spectroscopy in liquid and gas phase and Fiber Optics Coupled-Grazing Angle Probe-FTIR (FOCGAP-
FTIR) were used to characterize the spectroscopic signature of target threat agents. The surface experiments were
performed at detection levels of about 1 &mgr;g/cm2 suggest that limits of detection (LOD) achievable could be as low as
nanograms/cm2. Remote sensing experiments were performed using a telescope coupled with a Raman
spectrophotometer as a function of power and acquisition time. Characterization of compounds by vibrational
spectroscopy and the early stages of the transition from the lab based experiments to remote detection experiments will
be presented.
An actively operated standoff infrared detection system was designed from commercial infrared equipment: VECTOR 22 FTIR (Bruker Optics), an external mirror and an external MCT detector. One type of experiment was done for IR detection of high explosives RDX and TNT on reflective surfaces. In the detection on surface, the samples were move to different distances and a beam of infrared light was reflect on surface in angle of ~ 0° (backward collection from surface normal). First the samples: 2 to 30 μg/cm2 of high explosives TNT and RDX were characterized after depositing on stainless steel reflective surfaces using Reflection-Absorption Infrared Spectroscopy (RAIS). Then targets were moved to increasing distances: 3 to 12 feet and remote-sensed spectra were collected in active reflectance mode. The limits of detection were determined for all distances measured in both nitroexplosives. Limit of detection of 18 and 20 μg/cm2 for TNT and RDX respectively in the longest distances measured.
We report the preparation of explosives nanoparticles of RDX and TNT in a variety of substrates that include glass,
silicon and stainless steel. The explosive nanoparticles were prepared by means of pneumatically assisted
nebulization (PAN) using an electrospray (ESI) needle, which allowed for the direct deposit of the energetic material
onto the substrate. The deposited nanoparticles were characterized by optical microscopy, Scanning Electron
Microscopy (SEM), Energy Dispersive X-ray analysis (EDX) and Raman Microscopy. SEM micrographs showed
that the process produced particles with a mean size in the range of 80-500 nm and a narrow size distribution. For
TNT, the process produced smaller particles with a narrower size distribution. The EDX spectrum showed the
presence of carbon, nitrogen and oxygen consistent with the elemental composition of the energetic materials. The
chemical properties of the nanoparticles were also determined by vibrational spectroscopy.
Peroxide-based explosives have become of increased interest mainly because they are easily prepared and are not detected by traditional detection devices. The thermal behavior of triacetone triperoxide (TATP), a cyclic peroxide explosive was characterized by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). Dynamic and isothermal methods were used to characterize the sublimation process and to measure the vapor pressure at a temperature range under exothermic decomposition. The enthalpy of sublimation and kinetic parameters were estimated from direct mass loss rate measurements. Melting point, decomposition temperature and enthalpies of transitions were determined and compared to other known materials. The values were also compared to other recently reported values. The results of this study will help in the development of standoff detection technologies for improvised explosive devices using peroxide based materials.
Fiber Optic Coupled/Grazing Angle Probe Fourier Transform Infrared Spectroscopy has made possible to develop new methods for detection of traces of chemical compounds on surfaces. Thermal Inkjet Technology is able to deposit very small amounts of chemical compounds, including energetic materials, in a specific location on a surface. Aliquots of TNT solutions were deposited on stainless steel film. A thin coating of TNT can be produced by controlling the concentration of TNT, the number of drops dispensed and the distribution of drops over the surface. A Vector 22, a Bruker Optics FTIR fiber coupled to a Remspec Corp. grazing angle head was used for the experiments. The spectra were recorded at 4 cm-1 resolution and 50 scans. The results of the experiments gave intense absorption bands in the fingerprint region of the infrared spectra that were used for quantification. Chemometrics routines were applied in the enhancement of the quantitative analysis.
The objective of this research is to design and develop a multi-sensor capable of fast detection and of recognition optimization of the techniques for used for quantification of TATP by Pattern Recognition. In particular, the long range goal of the research is to use sensor fusion and sensor “talking” modalities to couple Stand Off detectors with Chemical Point detectors for detection of airborne chemical agents and detection of Improvised Explosive Devices (IEDs). Vibrational spectroscopy techniques are very fast and can be used for real time detection. Good results have been obtained with various target molecular (chemical) systems such as TATP, TNT and DNT. Samples of TATP were detected and quantified in air, in solution and in solid phase on surfaces by different techniques. FTIR Spectroscopy and GS-MS were used to generate new analytical procedures for detection and analysis of the organic peroxide. These procedures were compared and taken to their limits by optimization with Chemometrics, Partial Least Squares (PLS), and Discriminant Analysis (DA).
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