Existing instrumental techniques must be adaptable to the analysis of novel explosives if science is to keep up with the practices of terrorists and criminals. The focus of this work has been the development of analytical techniques for the analysis of two types of novel explosives: ascorbic acid-based propellants, and improvised mixtures of concentrated hydrogen peroxide/fuel. In recent years, the use of these explosives in improvised explosive devices (IEDs) has increased. It is therefore important to develop methods which permit the identification of the nature of the original explosive from post-blast residues. Ascorbic acid-based propellants are low explosives which employ an ascorbic acid fuel source with a nitrate/perchlorate oxidizer. A method which utilized ion chromatography with indirect photometric detection was optimized for the analysis of intact propellants. Post-burn and post-blast residues if these propellants were analyzed. It was determined that the ascorbic acid fuel and nitrate oxidizer could be detected in intact propellants, as well as in the post-burn and post-blast residues. Degradation products of the nitrate and perchlorate oxidizers were also detected. With a quadrupole time-of-flight mass spectrometer (QToFMS), exact mass measurements are possible. When an HPLC instrument is coupled to a QToFMS, the combination of retention time with accurate mass measurements, mass spectral fragmentation information, and isotopic abundance patterns allows for the unequivocal identification of a target analyte. An optimized HPLC-ESI-QToFMS method was applied to the analysis of ascorbic acid-based propellants. Exact mass measurements were collected for the fuel and oxidizer anions, and their degradation products. Ascorbic acid was detected in the intact samples and half of the propellants subjected to open burning; the intact fuel molecule was not detected in any of the post-blast residue. Two methods were optimized for the analysis of trace levels of hydrogen peroxide: HPLC with fluorescence detection (HPLC-FD), and HPLC with electrochemical detection (HPLC-ED). Both techniques were extremely selective for hydrogen peroxide. Both methods were applied to the analysis of post-blast debris from improvised mixtures of concentrated hydrogen peroxide/fuel; hydrogen peroxide was detected on variety of substrates. Hydrogen peroxide was detected in the post-blast residues of the improvised explosives TATP and HMTD.

Detection canines represent the fastest and most versatile means of illicit material detection. This research endeavor in its most simplistic form is the improvement of detection canines through training, training aids, and calibration. This study focuses on developing a universal calibration compound for which all detection canines, regardless of detection substance, can be tested daily to ensure that they are working with acceptable parameters. Surrogate continuation aids (SCAs) were developed for peroxide based explosives along with the validation of the SCAs already developed within the International Forensic Research Institute (IFRI) prototype surrogate explosives kit. Storage parameters of the SCAs were evaluated to give recommendations to the detection canine community on the best possible training aid storage solution that minimizes the likelihood of contamination. Two commonly used and accepted detection canine imprinting methods were also evaluated for the speed in which the canine is trained and their reliability. As a result of the completion of this study, SCAs have been developed for explosive detection canine use covering: peroxide based explosives, TNT based explosives, nitroglycerin based explosives, tagged explosives, plasticized explosives, and smokeless powders. Through the use of these surrogate continuation aids a more uniform and reliable system of training can be implemented in the field than is currently used today. By examining the storage parameters of the SCAs, an ideal storage system has been developed using three levels of containment for the reduction of possible contamination. The developed calibration compound will ease the growing concerns over the legality and reliability of detection canine use by detailing the daily working parameters of the canine, allowing for Daubert rules of evidence admissibility to be applied. Through canine field testing, it has been shown that the IFRI SCAs outperform other commercially available training aids on the market. Additionally, of the imprinting methods tested, no difference was found in the speed in which the canines are trained or their reliability to detect illicit materials. Therefore, if the recommendations discovered in this study are followed, the detection canine community will greatly benefit through the use of scientifically validated training techniques and training aids.

<div>Understanding the fundamental physics involved in the high strain rate deformation of high explosives (HE) is critical for developing more efficient, reliable, and safer energetic materials. When HE are impacted at high velocities, several thermo-mechanical processes are activated, which are responsible for the ignition of these materials. These processes occur at different time and length scales, some of them inaccessible by experimentation. Therefore, computational modeling is an excellent alternative to study multiscale phenomena responsible for the ignition and initiation of HE. This thesis aims to develop a continuum model of HMX to study the anisotropic behavior of HE at the mesoscale, including fracture evolution and plastic deformation. This thesis focus on three types of simulations. First, we investigate dynamic fracture and hotspot formation in HMX particles embedded in Sylgard binder undergoing high strain rate compression and harmonic excitation. We use the phase field damage model (PFDM) to simulate dynamic fracture. Also, we implement a thermal model to capture temperature increase due to fracture dissipation and friction at both cracks and debonded HMX/Sylgard interface. In our simulations, we observe that crack patterns are strongly dominated by initial defects such as pre-existing cracks and interface debonding. Regions with initial debonding between HMX particles and the polymer are critical sites where cracks nucleate and propagate. Heating due to friction generates in these regions too and caused the formation of critical hotspots. We also run simulations of a HMX particle under high-frequency harmonic excitation. As expected, higher frequencies and larger amplitudes lead to an increase in the damage growth rate. The simulations suggest that the intensity of the thermal localization can be controlled more readily by modifying the bonding properties between the particle and the binder rather than reducing the content of bulk defects in the particle. </div><div><br></div><div>Second, we present simulations of shock compression in HMX single crystals. For this purpose, we implemented a constitutive model that simulates the elastoplastic anisotropic response of this type of material. The continuum model includes a rate-dependent crystal plasticity model and the Mie-Gruneisen equation of state to obtain the pressure due to shock. Temperature evolves in the material due to plastic dissipation, shock, and thermo-elastic coupling. The model is calibrated with non-reactive atomistic simulations to make sure the model obeys the Rankine-Hugoniot jump conditions. We compare finite element (FE) and molecular dynamic (MD) simulations to study the formation of hot spots during the collapse of nano-size void in a HMX energetic crystal. The FE simulations captured the transition from viscoelastic collapse for relatively weak shocks to a hydrodynamic regime for strong shocks. The overall temperature distributions and the rate of pore collapse are similar to MD simulations. We observe that the void collapse rate and temperature field are strongly dependent on the plasticity model, and we quantify these effects. We also studied the collapse of a micron size void in HMX impacted at different crystal orientations and impact velocities. The simulation results of void collapse are in good agreement with a gas gun void collapse experiment. While the void size and crystal orientation do not affect the area ratio rate, they strongly affect the void collapse regime and temperature. Also, increased plastic activity when the crystal is impacted on the plane (110) renders higher temperature fields.</div><div><br></div><div>Finally, we studied shock compression and dynamic fracture in polycrystalline HMX using the same model implemented for shocks in single crystals. The goal of this study is to understand the role of crystal anisotropy and how it affects other hotspot formation mechanisms such as frictional heating. To simulate fracture, we used a phase field damage model implemented for large deformations. We first perform simulations of sustained shocks in polycrystalline HMX, where the grains are perfectly bonded to understand the effect of plastic deformation and hotspot formation due to plastic heating. Then, we simulate shocks in polycrystalline HMX with dynamic fracture. Simulations capture fracture evolution and frictional heating at cracks. In the polycrystalline case, we study heat generation due to shock and plastic deformation. A heterogeneous temperature field forms when the shock wave travels in the material. Temperature increases more in crystals that showed a higher magnitude of accumulated slip. When weak grain boundaries are included in the simulations, frictional heating becomes the dominant hotspot formation mechanism. As the crystals' interfaces break and crack surface sliding occurs, temperature increases due to friction at cracks. Hotspots tend to form at cracks oriented 45 deg from the shock direction. For this case, crystal anisotropy does not play an important role in temperature generation due to plastic dissipation. However, the random orientation of the crystals creates heterogeneous deformation and stress fields that cause the formation of a higher number of hotspots than the case where all the grains are oriented in the same direction.</div>

Before an IED is sent to a laboratory for analysis, it needs to be rendered safe if it did not already initiate. Render safe procedures (RSPs) include utilizing a percussion-actuated non-electric (PAN) disrupter or a mineral water bottle disrupter. Each disrupter utilizes explosives to render the device safe by breaking open the container or disrupting the fuzing system. However, the same explosives used in the RSP are also used by criminals in IED construction. As such, the explosives used in the RSP can cause problems with the interpretation of the results from forensic analysis of the IED fragments. Compounds of analytical interest in residue include nitroglycerin (NG), diphenylamine (DPA), ethyl centralite (EC), methyl centralite (MC), and pentaerythritol tetranitrate (PETN). Instrumentation used in the analysis of the residues included a gas chromatograph/mass spectrometer (GC/MS), a liquid chromatograph/mass spectrometer (LC/MS), and a gas chromatograph with an electron capture detector (GC/ECD). The PAN disrupter smokeless powder contained NG, DPA, and EC while the bulk detonation cord contained PETN. Only DPA decomposed after being burned. No residue was detected on the PVC pipes while residue was detected on the steel pipes and backpack mock IEDs. Overall, finding such residue in casework should not rule out the possibility that an individual used a particular explosive in the construction of the IED, but examiners should be aware of residues left by disrupters especially if the device initiates during the RSP.

This research aims to contribute to the safe methodology for additive manufacturing (AM) of energetic materials. Coating formulation processes were investigated to find a suitable method that may enable selective laser sintering (SLS) as the safe method for fabrication of high explosive (HE) compositions. For safety and convenience reasons, the concept demonstration was conducted using inert explosive simulants with properties quasi-similar to the real HE. Coating processes for simulant RDX-based microparticles by means of PCL and 3,4,5- trimethoxybenzaldehyde (as TNT simulant) are reported. These processes were evaluated for uniformity of coating the HE inert simulant particles with binder materials to facilitate the SLS as the adequate binding and fabrication method. The critical constraints being the coating effectiveness required, spherical particle morphology, micron size range (>20 μm) and a good powder deposition and flow, and performance under SLS to make the method applicable for HEs. Of the coating processes investigated, suspension system and single emulsion methods gave required particle near spherical morphology, size and uniform coating. The suspension process appears to be suitable for the SLS of HE mocks and potential formulation methods for active HE composites. The density was estimated to be comparable with the current HE compositions and plastic bonded explosives (PBXs) such as C4 and PE4, produced from traditional methods. The formulation method developed and the understanding of the science behind the processes paves the way toward safe SLS of the active HE compositions and may open avenues for further research and development of munitions of the future. / Dissertation (MSc (Applied Science:Chemical Technology))--University of Pretoria, 2019. / Chemical Engineering / MSc (Applied Science:Chemical Technology) / Unrestricted

Elemental analysis in forensic laboratories can be tedious and many trace evidence items are not analyzed to determine their elemental composition. Presently, scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS) is the primary analytical tool for determining the elemental composition of trace evidence items. However, due to the time it takes to obtain the required vacuum and the limited number of samples that can be analyzed at any one time, SEM-EDS can be impractical for a high volume of evidence items. An alternative instrument that can be used for this type of analysis is laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). While LA-ICP-MS is a very precise and quantitative analytical method that determines elemental composition based on isotopic mass measurements; however, the instrumentation is relatively expensive and therefore is budgetarily prohibitive for many forensic laboratories. It is the purpose of this research to evaluate an inexpensive instrument that can potentially provide rapid elemental analysis for many forensic laboratories. Laser induced breakdown spectroscopy (LIBS) is an analytical method that meets these requirements and offers information about the elemental composition based on ionic, atomic and diatomic molecular emissions.

Triacetone Triperoxide (TATP) is a primary high explosive that can be synthesized using commercially available starting materials and has grown in use among terrorists over the past several years. Additives present in the precursors were investigated to see if they carry through the TATP synthesis and can be detected in the final product potentially aiding in the identification of the source. Additives identified in the acetones were also identified in pre-blast and in some post-blast samples. However, these additives are present in trace quantities relative to the TATP, which coupled with the volatility and short lifetimes of some of the additives in TATP samples limit their detection in pre-blast and post-blast material. TATP prepared with different acids in the laboratory could generally be discriminated by observing the change in composition of the headspace of the samples upon heating and by IMS analysis of the crystals. The analysis of TATP synthesized on a larger scale was compared to the laboratory results of pre-blast material and post-blast debris. As in the laboratory samples, organic additives were also detected in the large-scale pre-blast samples and the identification of the additives in post-blast debris was consistent with the results obtained in the laboratory detonations.

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This dissertation expounds growing insight of the electrospray droplet ionization mechanism following ablation of dried hydrophobic and hydrophilic molecules using femtosecond laser pulses and mass analysis of the gas phase ions. Both hydrophobic and hydrophilic molecules were laser vaporized into an electrospray solvent opposite in polarity revealing appreciable ion intensity for all samples in contrast to ESI-MS and DESI measurements were solubility of the analyte in the spray solvent is a prerequisite. Quantitative analysis of equimolar protein solutions was established using LEMS reporting over three decades of quantitave response with little evidence of ion suppression. In contrast, ESI-MS measurements of similar equimolar protein solutions revealed severe ion suppression eliminating ion current from one of the protein analytes. Finally, the nature of an analyte following nonresonant laser vaporization has been the subject of debate. Aqueous trypsin was laser vaporized into an electrospray solvent containing either buffer or acid with substrate. LEMS measurements using buffer revealed enzyme-substrate intermediate charge states and continued enzymatic activity while the lack of enzyme-substrate intermediates and stymied enzymatic activity observed using acid suggests nonresonant laser vaporization preserves solution phase structure. This dissertation also extends considerably the use of LEMS for identification and characterization of energetic materials in their pre- and post-blast forms without sample preparation. The use of mulivarate analysis for the classification of large sample sets was also demonstrated showing high fidelity assignment of commercial formulations to their manufacturer. Five unburnt smokeless powders investigated using LEMS revealed unique combinations of organic molecules such as stabilizers and plasticizers using a simple electrospray solvent. Principal component analysis (PCA) provided exact classification of the mass spectra with respect to the manufacturer of the ordinance. LEMS measurements were then obtained from five commercial gunshot residue samples, or post-blast smokeless powder, revealing trace amounts of organics such as the stabilizers and large quantities of inorganic barium originating from the primer. Principal component analysis (PCA) again provided exact classification of the gunshot residue mass spectra with respect to the manufacturer of the ordinance. The use of a common transition metal complexation agent enabled full characterization of eight gunshot residue samples to include the heavy metals contained in the primer and the organics such as the stabilizers and plasticizers without any sample preparation or pre-concentration procedures. Principal component analysis (PCA) again provided high fidelity classification of the gunshot residue mass spectra with respect to the manufacturer of the ordinance after mass analysis with LEMS. Finally, highly energetic formulations such as composition 4 (C-4) and detonation cord subjected to nonresonant femtosecond laser vaporization enabled full characterization of these complex compositions identifying binders, stabilizers, the explosive ingredient and age-related decomposition derivative signature molecules with appreciable ion current detected using both positive and negative ion modes. / Chemistry