Thermite compounds have received a renewed interest due to their ability to store large quantities of energy that is comparable to conventional energetic materials. Such reactive materials can be manipulated to create a nanolaminated structure. It has been shown that an increase in the fraction of nanolaminated particles can reduce the ignition temperature and increase reactivity. In the present study, methods to lower the ignition temperature of aluminium copper-oxide (Al-CuO) are assessed. Arrested reactive milling (ARM) was used on stoichiometric Al-CuO powders to increase the nanolamination and reduce the ignition temperature to 840 Kelvins (K). Milling alone not only reduced the ignition temperature slightly, but for milling times greater than 30 minutes, intermediate phases were produced, which had negative impacts on the reaction characteristics. Another method to reduce the ignition temperature of Al-CuO involved creating a hybrid mixture using a compound with a lower ignition temperature to further decrease the ignition temperature of Al-CuO. ARM was used to lower the ignition temperature of a nickel aluminium (Ni-Al) intermetallic compound down to 480 K. Hybrid mixtures were then created with varying concentrations of milled and unmilled Al-CuO-Ni. Powders were then tested in a tubular furnace to determine the ignition temperature dependence on heating rate and concentration of constituents. It has been shown that an unmilled hybrid mixture with 75% and 50% concentration of Al-CuO has an ignition temperature of 840 K. Higher concentrations of Ni-Al resulted in lowered ignition temperatures which varied between 600 K and 480 K. A milled hybrid mixture has lower ignition temperatures than an unmilled mixture. It was shown that a milled hybrid mixture with a 75% concentration of Al-CuO has an ignition temperature of 840 K, corresponding to pure Al-CuO. The ignition temperature of the milled hybrid mixture was reduced to approximately 520-620 K for concentrations of Ni-Al of 50%, and 473-573 K for concentrations of 75% Ni-Al.

Reactive material liners paired with high explosives can significantly increase blast effects. This research aims to study the properties that primarily control the interaction between reactive materials (RM) and high explosives (HE). This will facilitate blast performance optimization for the RM and HE combinations. A laser spectroscopic sensor will be utilized to measure the performance of these RM and HE combinations. Laser absorption spectroscopy (LAS) is a technique that measures the chemical concentration of a medium through the intensity change of the laser beam. The laser diagnostic instrument is composed of two tunable diode lasers, one centered at 2.48 μm and the other at 2.55 μm. The sensor is designed to measure H2O species concentration in the blast wave using the beer-lambert law. It will also measure the temperature of the blast with a high temperature sensitivity in the 1000 K to 2600 K range. The temperature and concentration data will be used to assess the combustion performance of the blast. The data was collected at a 200 MHz sampling frequency through a fiber-coupled optical probe designed to shield the sensitive optical equipment. The resulting blast temperature and molar concentration of H2O will be used to determine the optimal RM liner and HE pairings in the MMRT chamber. This research will enable the AFRL to expand their understanding of the RM and HE pairings.

The research herein presents an approach to stabilising reactive materials by engineering and designing strategies for forming multi-component materials containing the reactive molecules by use of their non-covalent intermolecular interactions. These interactions may be utilised as part of a design approach to create new materials of more beneficial physical and chemical properties for the desired application. The reactive materials focussed on in this research are organic peroxyacids, in particular peroxyacetic acid, meta-chloroperbenzoic acid and 6-phthalimidoperoxyhexanoic acid. The stabilities of these target materials under different conditions are probed to find a suitable environment for crystallisation experiments. Crystal structures of the materials were isolated and characterised and the peroxyacids were subsequently cocrystallised with materials chosen to interact with the target molecules to form new molecular complexes, including carboxylic acids, π stacking materials and metal salts. A hosting approach was also employed to form multi-component systems containing these materials, crystallising them with larger, stable, structure-generating compounds with the aim of intercalating the reactive molecules in their stable structure. To this end, urea based compounds, cyclodextrins and Montmorillonite clay were investigated as hosting materials. Candidate multi-component materials were synthesised which successfully retain peroxyacid reactivity. A second set of materials studied was agrichemicals, which also frequently have reactive character, in which a change in physical properties was pursued by the method of forming new crystalline complexes. Five new crystalline agrochemical molecular complexes were synthesised and tested for thermal stability in comparison to the original materials to assess for changes in properties of the multi-component materials.

There is a need for simulation methodologies for multiphase three-dimensional microstructures that can be used in numerical simulations of material behavior or in exact computation of effective properties using microstructural correlation functions. Specifically, the methodology must be able to generate verifiably realistic microstructures, with complex morphology accurately represented. Striving to address that need, the research presented here develops a general microstructure simulation toolbox for multiphase two- and three-dimensional microstructures consisting of one connected phase and one or more particulate phases. Previous work by other researchers has found successful solutions to a variety of special cases of the general problem, but most of them are intended for binary microstructures, and nearly all simulate only two-dimensional microstructures. The toolbox presented here attempts to exceed those limitations. Its framework is a Metropolis stochastic-optimization routine running a simulated-anneal schedule, with particle position coordinates defining the configuration space and a range of forms available for the ﾓenergyﾔ? function. The toolbox allows several parameterizations of the microstructure, supplying all elementary properties (phase volume fractions, mean sizes, etc.) and some non-elementary properties (distributions of elementary properties, properties relating to inter-phase distances and morphology) of microstructures as possible parameters. The toolbox is able, as one special case, to simulate realistic microstructures of uniaxially compacted mixtures of elemental Al-Ti-B powders and achieve basic microstructure-processing correlation. Statistical tests involving microstructural correlation functions bear out the realism. The toolbox is also able to generate virtual microstructures for the same system, for use in the design of experiments (which are in fact high-strain-rate impact simulations), and for evaluating hypotheses involving achievable material properties. The Al-Ti-B powder compacts are potential advanced energetic materials that, when subjected to high-strain-rate impact (which may or may not constitute shock compression), explosively release heat by anaerobic reaction according as certain incompletely understood conditions are met or not. The study of those conditions and the mechanism of reaction initiation (carried out by a collaborator) is the specific application that the simulations in this work cater to. To ensure realistic morphology in simulated Al-Ti-B microstructures, this work included reconstruction (carried out by montage serial sectioning) of large three-dimensional volumes of Al-Ti and Al-B binary compacts for two sets of powders that yielded actual 3 D Ti and B particle images. Accordingly, advancement of the experimental technique of montage serial sectioning and a quantitative characterization of the real powder microstructures also formed part of this research. While only examples from Al-Ti-B powders are used throughout this work, it is clear that the methods will apply to other similar systems.

Silicones are industrially important polymers characterized by a wide spectrum of chemical and physical properties with a number of important applications including automotive components, construction materials, isolating parts in electronic devices, flexible electronics, and medical products. Development of additive manufacturing methods for silicones enable production of complex and custom designed shapes and structures at both the micro- and macro-scale, economically feasible. In general, such materials can be fabricated using stereolithographic, extrusion-based, or inkjet printing techniques, in which silicones are polymerized using either photo- or heat-initiators. Silicones can also be crosslinked based on chemical reactions. Although this approach is supposedly the simplest, it has not been widely applied in additive manufacturing, as suitable technology for mixing and curing reactive inks without clogging nozzles has not be developed yet. To address this issue, a new 3D printer, that enables the fabrication of highly reactive and low viscous materials, has been developed and tested experimentally. The proposed fabrication method involves the ejection of two reactive droplets simultaneously from individual dispensers, merging and mixing them in free space outside the nozzle followed by deposition of the merged drop in a patterned format on a substrate. It was shown that the printing process is robust and stable more than 4 hours and it can be used on demand. By incorporating an XYZ positioner, it was possible to deposit droplets in an overlapping fashion to print any programmable shape featuring homogeneous structure, with a small number of pores. Moreover, due to the almost instantaneous reaction between two components (< 10s), the fabrication of very high aspect ratio (AR > 50) objects is possible. Lastly, the presented method can be easily adapted to print in free space without the use of support materials. / Thesis / Master of Applied Science (MASc)

Structural energetic materials (SEM) are a class of multicomponent materials which may react under various conditions to release energy. Fragmentation and impact induced reaction are not well characterized phenomena in SEMs. The structural energetic systems under consideration here combine aluminum with one or more of the following: nickel, tantalum, tungsten, and/or zirconium. These metal+Al systems were formulated with powders and consolidated using explosive compaction or the gas dynamic cold spray process. Fragment size distributions of the indicated metal+Al systems were explored; mean fragment sizes were found to be smaller than those from homogeneous ductile metals at comparable strain rates, posing a reduced risk to innocent bystanders if used in munitions. Extensive interface failure was observed which suggested that the interface density of these systems was an important parameter in their fragmentation. Existing fragmentation models for ductile materials did not adequately capture the fragmentation behavior of the structural energetic materials in question. A correction was suggested to modify an existing fragmentation model to expand its applicability to structural energetic materials. Fragment data demonstrated that the structural energetic materials in question provided a significant mass of combustible fragments. The potential combustion enthalpy of these fragments was shown to be significant. Impact experiments were utilized to study impact induced reaction in the indicated metal+Al SEM systems. Mesoscale parametric simulations of these experiments indicated that the topology of the microstructure constituents, particularly the stronger phase(s), played a significant role in regulating impact induced reactions. Materials in which the hard phase was topologically connected were more likely to react at a lower impact velocity due to plastic deformation induced temperature increases. When a compliant matrix surrounded stronger, simply connected particles, the compliant matrix accommodated nearly all of the deformation, which limited plastic deformation induced temperature increases in the stronger particles and reduced reactivity. Decreased difference between the strength of the constituents in the material also increased reactivity. The results presented here demonstrate that the fragmentation and reaction of metal+Al structural energetic materials are influenced by composition, microstructure topology, interface density, and constituent mechanical properties.

The focus of this work is on the modeling and simulation of shock wave propagation in reactive metal powder mixtures. Reactive metal systems are non-explosive, solid-state materials that release chemical energy when subjected to sufficiently strong stimuli. Shock loading experiments have demonstrated that ultra-fast chemical reactions can be achieved in certain micron-sized metal powder mixtures. However, the mechanisms of rapid mixing that drive these chemical reactions are currently unclear. The goal of this research is to gain an understanding of the shock-induced deformation that enables these ultra-fast reactions. The problem is approached using direct numerical simulation. In this work, a finite element (FE) model is developed to simulate shock wave propagation in discrete particle mixtures. This provides explicit particle-level resolution of the thermal and mechanical fields that develop in the shock wave. The Ni/Al powder system has been selected for study. To facilitate mesoscale FE simulation, a new dislocation-based constitutive model has been developed to address the viscoplastic deformation of fcc metals at very high strain rates. Six distinct initial configurations of the Ni/Al powder system have been simulated to quantify the effects of powder configuration (e.g., particle size, phase morphology, and constituent volume fractions) on deformation in the shock wave. Results relevant to the degree of shock-induced mixing in the Ni/Al powders are presented, including specific analysis of the thermodynamic state and microstructure of the Ni/Al interfaces that develop during wave propagation. Finally, it is shown that velocity fluctuations at the Ni/Al interfaces (which arise due to material heterogeneity) may serve to fragment the particles down to the nanoscale, and thus provide an explanation of ultra-fast chemical reactions in these material systems.

No description available.

This work presents a systematic study of the mechanochemical processes leading to chemical reactions occurring due to effects of high-strain-rate deformation associated with uniaxial strain and uniaxial stress impact loading in highly heterogeneous metal powder-based reactive materials, specifically compacted mixtures of Ti/Al/B powders. This system was selected because of the large exothermic heat of reaction in the Ti+2B reaction, which can support the subsequent Al-combustion reaction. The unique deformation state achievable by such high-pressure loading methods can drive chemical reactions, mediated by microstructure-dependent meso-scale phenomena. Design of the next generation of multifunctional energetic structural materials (MESMs) consisting of metal-metal mixtures requires an understanding of the mechanochemical processes leading to chemical reactions under dynamic loading to properly engineer the materials. The highly heterogeneous and hierarchical microstructures inherent in compacted powder mixtures further complicate understanding of the mechanochemical origins of shock-induced reaction events due to the disparate length and time scales involved. A two-pronged approach is taken where impact experiments in both the uniaxial stress (rod-on-anvil Taylor impact experiments) and uniaxial strain (instrumented parallel-plate gas-gun experiments) load configurations are performed in conjunction with highly-resolved microstructure-based simulations replicating the experimental setup. The simulations capture the bulk response of the powder to the loading, and provide a look at the meso-scale deformation features observed under conditions of uniaxial stress or strain. Experiments under uniaxial stress loading reveal an optimal stoichiometry for Ti+2B mixtures containing up to 50% Al by volume, based on a reduced impact velocity threshold required for impact-induced reaction initiation as evidenced by observation of light emission. Uniaxial strain experiments on the Ti+2B binary mixture show possible expanded states in the powder at pressures greater than 6 GPa, consistent with the Ballotechnic hypothesis for shock-induced chemical reactions. Rise-time dispersive signatures are consistently observed under uniaxial strain loading, indicating complex compaction phenomena, which are reproducible by the meso-scale simulations. The simulations show the prevalence of shear banding and particle agglomeration in the uniaxial stress case, providing a possible rationale for the lower observed reaction threshold. Bulk shock response is captured by the uniaxial strain meso-scale simulations and is compared with PVDF stress gauge and VISAR traces to validate the simulation scheme. The simulations also reveal the meso-mechanical origins of the wave dispersion experimentally recorded by PVDF stress gauges.