The ReaxFF method provides a highly transferable simulation method for atomistic scale simulations on chemical reactions at the nanosecond and nanometer scale. It combines concepts of bond-order based potentials with a polarizable charge distribution.
Since it initial development for hydrocarbons in 2001, we have found that this concept is transferable to applications to elements all across the periodic table, including all first row elements, metals, ceramics and ionic materials. For all these elements and associated materials we have demonstrated that ReaxFF can accurately reproduce quantum mechanics-based structures, reaction energies and reaction barriers, enabling the method to predict reaction kinetics in complicated, multi-material environments at a relatively modest computational expense.
This presentation will describe the current concepts of the ReaxFF method, the current status of the various ReaxFF codes, including parallel implementations. Also, we will present and overview of recent applications to a range of materials of increasing complexity, with applications to combustion, catalysis, aqueous phase chemistry and material failure. Two particular focal points of this presentation will include:
1) Recent applications of ReaxFF to battery materials - including carbon and silicon anodes and reactions at their interfaces with electrolytes
2) Combustion reactions - including gas-phase combustion as well as combustion events catalyzed by metal and mixed metal oxide surfaces. Here we will also adress recent improvements in the ReaxFF description for the mechanical properties of graphitic materials and applications to high-temperature soot formation.

Intermolecular reactive composites find diverse applications in defense, microelectronics and medicine, where strong, localized sources of heat are required. However, fundamental questions of the initiation and propagation mechanisms on the nanoscale remain to be addressed, which is a roadblock to their widespread application. The performance and response of these materials is predominantly influenced by their nanostructure, and the complex interplay of mechanical, thermal and chemical processes that occur at very short time scales. Motivated by experimental work which has shown that high-energy ball milling can significantly improve the reactivity as well as the ease of ignition of Ni/Al inter-metallic composites, we present large scale (~41 million atom) molecular dynamics simulations of shock-induced chemistry in granular Ni/Al nano-composites, which are designed to capture the microstructure that is obtained post milling. Shock propagation in these granular composites is observed to be extremely diffuse at low piston velocities, leading to a large inhomogeneity in the local stress states of the material. At higher piston velocities, the shock front is more homogeneous as a consequence of a change in the pore compaction mechanism; from plastic deformation mediated pore collapse at low piston velocities, to fluid filling of the pores at higher impact velocities. The flow of molten ejecta into the pores subsequently leads to the formation of vortices, where the reaction progresses much faster than in the bulk. While it has been understood for a while now that pores act as initiation sites through the localization of thermal energy, we find that vortex formation in the pores leads to the localization of both thermal and translational kinetic energy, which has consequences both during the initiation process and in the development of the reaction fronts that propagate outwards from the pores. We also follow the evolution of the chemistry to completion after the passage of the shock by allowing the sample to ‘cook&’ under the shock induced pressures and temperatures for up to 0.5 ns. Multiple ‘tendril-like&’ reaction fronts, born in the cauldron of the pores, propagate rapidly through the sample, consuming it within a nanosecond.

Beside their relevance in commercial applications metallic multilayers also serve as model materials for exploring the metallurgical fundamentals of self-propagating reactions occurring in reactive materials. Here, we focus on ignition of those reactions by thermal heating. For that purpose, we have to study irreversible phase transformations under rapid heating conditions with heating rates heating rates of up to 10⁷ K/s. Recent in situ experiments suggest that three major factors influence the sequence of transformations that occur during these rapid reactions: the nature of the interfaces (solid/solid or solid/liquid), the heating rates and the maximum reaction temperature. The effect of heating rate is particularly important for reactions that remain in the solid state, like those taking place at the very beginning of thermal ignition. Here, we use thermodynamic and kinetic modelling of the first nucleation event in Al:Ni multilayer films as a function of heating rate to predict the first phase to form. The effort draws on the concept that steep concentration gradients impede nucleation. We use a closed analytical solution for the thermodynamic and numerical calculations for the kinetic modelling. This combined approach enables us to infer a heating rate regime where the kinetics of nucleation starts to dominate. Finally, we compare the predictions with recent experimental results.

A computational model of anaerobic reactions in metallic multilayered systems with an equimolar composition of zirconium and aluminum is developed. The reduced reaction formalism of Salloum and Knio [Combust. Flame 157:288-295, 2010] is adopted. Attention is focused on quantifying intermixing rates based on experimental measurements of uniform ignition as well as measurements of self-propagating front velocities. Estimates of atomic dffusivity are #64257;rst obtained based on a regression analysis. A more elaborate Bayesian inference formalism is then applied in order to assess the impact of uncertainties in the measurements, potential discrepancies between predictions and observations, as well as the sensitivity of predictions to inferred parameters. Intermixing rates are correlated in terms of a composite Arrhenius law, which exhibits a discontinuity around the Al melting temperature. Analysis of the predictions shown indicates that Arrhenius parameters inferred for the low-temperature branch lie within a tight range, whereas the parameters of the high temperature branch are characterized by higher uncertainty. The latter is due to scatter in the experimental measurements, and to the limited range of bilayers where observations are available. For both branches, the predictions exhibit higher sensitivity to the activation energy than the pre-exponent, whose posteriors are highly correlated.

In contrast to the traditional, purely hydrodynamic role of shock waves in the initiation of reaction, the role of dynamic shear in the initiation of reaction in heterogeneous powders capable of exothermic reaction has not been thoroughly characterized. In this study, the Thick Walled Cylinder (TWC) technique is employed to create a state of pure shear via the implosion of an annular sample of reactive composition. A gelled explosive with tunable density and detonation velocity is used to implode a copper outer driver tube, and a hollow inner copper tube arrests the implosion, thus determining the amount of shear applied. Heterodyne Doppler Velocimetry techniques are used on the driver tube inner wall to quantify the rate of application of shear and strength of the shock wave transmitted into the sample. Two compositions, Mn + S and Ti + 2B, that react with little or no generation of gaseous products and that have been previously characterized for shock initiation, are studied. The critical amount of shear required to initiate reaction is identified for the compositions. Analysis of post-shot samples from sub-critical experiments are examined via X-ray crystallography (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) to identify the features of shear localization that are responsible for reaction onset.

Self-propagating reactions of two or more elements are a known way to produce ceramic or intermetallic compounds. The reactants are commonly present as finely dispersed powders or multilayers, e.g. produced by PVD methods. While being expensive and complex, PVD methods offer unsurpassed control over composition, purity and interface geometry of the reactive system. These benefits make PVD the preferred sample production method in studies on characteristics of reaction and ignition.
A few years ago, it has been shown that the system Ru/Al is capable of self-propagation reactions. The resulting phase, B2-RuAl, shows a combination of properties not commonly observed in intermetallic compounds. While having a high melting point (>2030 °C) and good oxidation resistance, RuAl has been reported to exhibit room-temperature ductility. Its heat of formation and reaction front velocities make it comparable to Ni/Al reactive systems while showing a significantly higher reaction temperature of at least 1950 °C.
In this study, we investigate sputter-deposited Ru/Al multilayers regarding temperature and activation energy of ignition and phases involved in the ignition process. Microstructural investigations are carried out using FIB/SEM, TEM and atom probe tomography (APT). Results are discussed in relation with DSC measurements. We found ignition temperatures to range from 408°C to 608 °C for bilayer periods of 22 nm to 222 nm, respectively. Activation energy of the ignition reaction derived from these values is found to be similar to that reported for Ni/Al multilayers, indicating a similar mechanism.

The influence of accelerated ion beams on the microstructure and ignition behavior of Ni/Al reactive multilayer foils was investigated for the first time. The FN Tandem accelerator at University of Notre Dame was used to produce ion beams (¹⁶O, ¹²C and ²⁷Al) with different energies (25 - 50 MeV), charge states and intensities. It was shown that exposure of the foils (~100 nm in bilayer thickness and 6-8 mm in total thickness) by an oxygen beam leads to the oxidation of the surface of the foils, while carbon and aluminum beams did not change the chemical composition of the multilayer. It was shown that the minimum beam power sufficient to initiate the combustion of foils increases for lower Z beams (¹⁶O, ¹²C) compared to ²⁷Al. This might be explained by the energy loss of specific projectiles in target material. Microstructures of Ni/Al foils subjected to ion beam bombardment were investigated as a function of beam intensity and exposure duration. Transmission Electron Microscopy (TEM) evidences that irradiation of the foil at levels below the ignition threshold leads to substantial inter-diffusion and intermixing of metals. This effect resulted in the decrease of the thicknesses of Ni layers due to gradual solid-state dissolution of Ni into Al layers with the formation of compounds. For example, during the 90 min bombardment of the foils by ¹²C beam (0.27 Watt) the average thickness of Ni layers decreased from 45 nm to 25 nm while the thickness of Al layers increased from 50 to 60 nm. It should be noted that when Ni content in the Al layers reaches a critical content of 23 atomic percent the Al layers convert to Al₃Ni phase. The reactivity and combustion behaviors of bombarded Ni/Al foils are under investigation by calorimetric and imaging techniques and will be presented.

Over the last several decades, a variety of reactive materials have been conceived of, processed, and characterized resulting in a large body of data for these materials. However, to date, the majority of materials that have transitioned from basic research to application have been developed for the niche application with little understanding of the mechanisms that allow the reactive material to be successful. This limits the design capability for these materials. The major challenge for the future of these materials is developing theories and models that allow for the design of new reactive materials to meet specific application needs. These theories and models need to account for advancements in processing and microstructural control. Advancements in characterization will be required to validate the models and ensure the understanding of design margins. This presentation will review the state-of-the-art for understanding reactive materials and present possible paths for moving toward reactive materials by design.

For the purpose of not being eaten, biological organisms developed numerous defense mechanisms during evolution. For example, the bombardier beetle is able to emit a hot and repellent spray from its abdomen. The beetle carries the reactants hydrogen peroxide (H₂O₂) and hydroquinone in a reservoir and can squeeze them into a reaction chamber holding enzymes to degrade them. The resulting reaction is highly exothermic and due to gas formation, the enhanced pressure induces an explosive release of the products.¹ Inspired by this system, we developed a self-defending surface holding H₂O₂ and manganese dioxide in compartmented layers.² Upon rupture, the compounds mix and the catalyzed decomposition of H₂O₂ takes place resulting in hot foam. With this, a mechanical energy of 2-3 Joules triggers the release of chemical energy of several hundreds of Joules. As an application, we proposed the implementation in money security systems due to the increasing number of ATM incidents.³ We showed that an oxidation resistant dye allows labelling bank notes visually and renders them worthless in case of an ATM robbery. DNA encapsulated SiO₂ particles⁴ additionally mark the bills forensically. The presented system has an improvement by means of simplicity and cost compared to existing money protection systems which often bear pressured gas and color bottles.
1. Dean, J.; Aneshansley, D. J.; Edgerton, H. E.; Eisner, T., Defensive spray of the bombardier beetle - a biological pulse jet. Science 1990, 248, 1219-1221.
2. Halter, J. G.; Cohrs, N. H.; Hild, N.; Paunescu, D.; Grass, R. N.; Stark, W. J., Self-defending anti-vandalism surfaces based on mechanically triggered mixing of reactants in polymer foils. J. Mat. Chem. A 2014, 2, 8425-8430.
3. (EAST), E. A. S. T. ATM explosive attacks and low tech fraud incidents increase in Europe. www.european-atm-security.eu/Press%20and%20Media/
4. Paunescu, D.; Fuhrer, R.; Grass, R. N., Protection and deprotection of DNA-high-temperature stability of nucleic acid barcodes for polymer labeling. Angewandte Chemie-International Edition 2013, 52, 4269-4272.

Engineering nanocomposite materials are composed by heterogeneous mixtures of metallic fuels and inorganic oxidizers with nanoscale dimensions. This active field of research is driven by the development of multi-functional combustion systems with enhanced capabilities at low costs for applications in many fields including environmentally clean primers, in situ welding, thermal batteries and many others for both defense and civil purposes.
Among metallic fuel and inorganic oxidizer couples, Al/CuO is particularly interesting because of its high potential energy, tunable reactivity, its ability to produce gas at high temperature and its compatibility with MEMS technology.
It has been now widely demonstrated that at the nanoscale, the reactivity of such Al/CuO nanocomposites is significantly enhanced but depends on the organization, density, and dimensions of particles, which largely influence their combustion kinetics and overall thermal properties. Typically nanocomposite materials are processed in hexane solutions using ultrasonication with low volumetric loads of nanopowders. Ultrasonication is used to disperse agglomerates and increase mixing intimacy but this can form undispersed agglomerates of segregated particles during drying which may lead to inhomogeneity and a wider dispersion in combustion kinetics. To overcome this issue, a bottom-up approach through DNA-directed Al and CuO nanoparticles self-assembly is a good way to design and engineer nanocomposite materials with controlled composition and excellent homogeneity. In our previous work¹, we demonstrated the potential of DNA as a structural material to self-assemble Al and CuO nanoparticles. In this contribution, we will touch on the design of a DNA-directed self-assembly procedure to develop on one hand, reliable protocols to disperse and sort metallic and metal oxide nanopowders in an aqueous solution and on the other the establishment of specific DNA surface modification processes for Al and CuO.
The nature of the mechanisms driving DNA self-assembly was studied using several characterization techniques (Zeta Potential measurements, particle size analysis using DLS and electron microscopy). The aggregation kinetics depending on several parameters was also monitored and the structure of assembled objects analyzed by SEM and TEM imaging and EDX analysis. More importantly, we managed to obtain highly energetic Al/CuO nanocomposites with exquisite energetic performance. Another issue with nanocomposites is the direct deposition of the Al/CuO mixtures onto functional devices. In fact, direct ink deposition of nanocomposites using inkjet procedures may eliminate exposure to dry powders which are very sensitive and unsafe to manipulate. Moreover, we also explored the potential of DNA as a structural and preservative link for this kind of deposition.
¹Séverac, Fabrice, et al. "High#8208;Energy Al/CuO Nanocomposites Obtained by DNA#8208;Directed Assembly." Adv. Funct. Mater. 22.2 (2012): 323-329.

Functional nanomaterials are being produced by many different types of fabrication methodologies. The focus of the present paper is on the usage of such nanomaterials in reactive systems where the nanoscale structure and organization are used to control reaction and response characteristics of materials. Examples include the nanothermites, functionalized graphene sheets, and nanoporous silicon. Examples of various systems are given in the paper.

Nanostructured porous silicon prepared using galvanic etching in hydrofluoric acid has been widely used for on-chip energetic combustion applications. Previous efforts by us and other energetic porous silicon researchers have primarily focused on nanostructured pores impregnated with concentrated sodium perchlorate oxidizer in a methanol solution. The combustion performance is highly tunable through changes in material properties such as porosity and specific surface area, exhibits high energy density, and in some cases results in extremely rapid burn rates. However, sodium perchlorate is known to be moisture sensitive (hygroscopic). Therefore, a lack of reproducibility in combustion performance is experienced for aged materials. Other oxidizers, some of which may be less hygroscopic, have been explored in the past. But results have been limited to qualitative comparisons with little quantitative data.
For this reason, we are focusing on the preparation of porous silicon with alternative oxidizers and the quantification of reaction output. We are specifically studying sulfur, potassium periodates (KIO₄), sodium periodate (NaIO₄), and iodine pentaoxide (I₂O₅). With the use of various oxidizers, different pore loading techniques are necessary to achieve stable energetic systems. In the case of sulfur, we have successfully melted and directly filled the pores. Solution-deposited pore loading using different compatible solvents, depending on the oxidizer, will be used for other oxidizers. On-chip porous silicon materials with a range of specific surface areas between 200 - 900 m²_/g and porosities between 50 and 80% are used in this study. We have characterized the material properties of porous silicon using gas adsorption porosimetry and the Brunauer-Emmett-Teller (BET) theory, SEM and profilometry. We will quantify material stability before and after the pore loading process, and quantify reaction characteristics using high speed videography and bomb calorimetry, ultimately providing a quantitative comparison within different on-chip porous silicon/oxidizer systems. Additionally, alternative preparation of porous silicon by etching mechanically milled silicon particles will allow us to further quantify and compare the combustion performance of porous silicon/oxidizer systems, in both, on-chip and particle form.

For microscale on-chip combustion applications, small, closely oriented energy sources are desired for certain MEMS applications (e.g. heating, fuzing, micropropulsion, etc.). We have previously reported on the rapid combustion events of an on-chip porous silicon/sodium perchlorate energetic material with >3 km/s burn speeds, higher than many comparable reactive materials. Aside from very rapid combustion, this system is highly tunable and has demonstrated much slower burn speeds on the order of 1 m/s. The present study explores this slow regime of porous silicon combustion and its limits for on-chip applications. On-chip porous silicon energetics are embedded in crystalline silicon, and therefore are surrounded on three sides by an efficient thermal conductor. For slow burning systems, this presents complications as heat loss to the crystalline silicon substrate can result in inconsistent burning or flame extinction. We investigate <50 mu;m wide porous silicon strips, sparsely filled with sodium perchlorate (NaClO₄), to probe the limits of on-chip combustion. The porous silicon is patterned atop the silicon substrate in a manner that provides a winding pathway to demonstrate the ability of the material to change direction during propagation. This patterning also probes the minimum spacing that is required between porous silicon strips. We have demonstrated independent burning for two 50 mu;m wide porous silicon strips down to a strip spacing of ~25 mu;m. This small spacing allows for close packing of porous silicon strips and a potential burn path length of >25 cm on a 1.3x1.2 cm chip. This may produce adequate burn times to make porous silicon applicable as a future material for fuze delay timers, or as a thermal source with a relatively long duration in comparison to typical reactive materials.

The electric explosion wire technique for production of nanometals is presented. The main parameters, characteristics and features of electric explosion of wire process and results (kinds of nanoparticles and its applications) are discussed.
It is possible to produce bimetal nanoparticles with controlled content of metals within one particle. Bimetal nanoparticles were produced by simultaneous electrical explosion of two wires (Al and Cu). An alternative method to obtain bimetal nanoparticles is also suggested using a spontaneous electrochemical process from salt solutions. In the latter case, a thin film of Ni on the surface of nano-Al is obtained.
Bimetal nanoparticles (BMNP) for both Al-Cu and Al-Ni were prepared and studied.
The work studies the oxidation, ignition and thermal reactivity of the BMNP of Al-Cu and Al-Ni in a simultaneous thermogravimetric (TG) and differential scanning calorimetry (DSC) experiments. The microstructure is characterized with a scanning electron microscope (SEM) and transmission electron microscope (TEM). The phase compositions of the reaction products were investigated with X-ray diffraction. By comparing the peak temperature of the first exothermic reaction in DSC and the phase transition temperatures in the respective binary systems, it was found that for Al-Cu BMNP the melting of an alloy played a pivotal role for the early ignition reaction. The comparison of the reactivity of BMNP with that of nano Al particles shows that BMNP Al-Cu and Al-Ni were more reactive.

Among energetic materials, aluminum powders have a prominent position due to their use as a component in propellant formulations, explosives and pyrotechnics [1]. In all those applications, it is the highly exothermic reaction of aluminum with an oxidant that confers to the powders their reactive and propulsive properties. For such type of applications, there is a definitive interest in improving the reactivity of aluminum powders and the natural trend is to produce powders with a high specific surface area (higher than 10m2/g) i.e. aluminum nanopowders (Al-NPs).
Aluminum powders can be described within core-shell morphology. Each aluminum particles is covered by a thin alumina layer whose thickness does not vary much with the size of the aluminum core [2]. For low heating rate, the oxidation is controlled by a diffusion mechanism in which the alumina layer plays an important role due to its various polymorphic transitions [3]. The enhanced reactivity of Al-NPs is thus linked to the higher division state but also to the microstructural changes that plays an important role on the combustion process. It could be then interesting to vary morphology, surface area and nanostructure in order to elaborate the most efficient material.
In most cases, aluminum nanopowders are manufactured either by vapor phase condensation or by liquid state chemistry and they have a spherical morphology. In this contribution, a reactive mechanical milling approach is proposed for the synthesis of highly reactive aluminum nanoflakes. Although being largely used for manufacturing nanocrystalline metals or nanocomposites using arrested reactive milling, to our knowledge, mechanical milling has never been used to optimize the reactivity of pure aluminum powders. This is maybe linked to the fact that, due to their ductility, it is very difficult to increase their specific surface area by this procedure. Thanks to a reactive milling procedure where air is introduced in a controlled way, we will show in this contribution how it is possible to increase the specific surface area of the powders and to modify the microstructure of the aluminum particles [4]. A comparative study between spherical nanopowders and nanoflakes will be presented owing to various characterization techniques such as high resolution transmission Electron microscopy, neutrons and X-ray diffraction and thermal analyses. It is shown that morphology and the microstructure are important parameters that influence the reactivity.
[1] Dreizin E. L., Prog. Energy Combust. Sci. 35 (2009) 141.
[2] Rufino B. et al. Acta Mater. 55 (2007) 2815.
[3] Trunov, M. A. et al. Combust. Flame 140 (2005), 310.
[4] André B. et al, Mat. Lett. 110 (2013) 108
Acknowledgments :
Agence Nationale de la Recherche and Direction Générale des Armées are aknowledged for financial support (Grant No ANR-13-ASTR-0032).

Because of the high energy density, easy ignition, and good storability, mechanically alloyed Al/Mg powder has the potential to improve the performance characteristics of various energetic and gas-generating materials. In the present talk, we report our recent results on the use of this powder in combustible mixtures for generation of oxygen and hydrogen. The mixtures for oxygen generation consisted of sodium chlorate, nanoscale cobalt oxide catalyst, and Al/Mg (1:1 mass ratio) powder, while those for hydrogen generation included water, polyacrylamide as a gellant, and Al/Mg powder. To increase hydrogen yield, ammonia borane (NH₃BH₃) was also added to Al/Mgminus;water mixtures. Combustion experiments were conducted in an argon environment, using laser ignition. The thermal wave propagation over the oxygen-generating mixtures was studied using infrared video recording. It has been shown that mechanically alloyed Al/Mg material is a promising alternative to iron and tin, currently used as fuels in chemical oxygen generators, because significantly smaller amounts of this additive are needed for a steady propagation of the combustion wave. The hydrogen generation experiments have shown that mixtures of mechanically alloyed Al/Mg powder with 10minus;60 wt% gelled water are combustible, with the front velocities exceeding the values obtained for the mixtures of water with nanoscale Al. Hydrogen yield was measured using mass-spectrometry. In the mixtures that included ammonia borane, D₂O was used instead of H₂O. Measurements of H₂, D₂, and HD concentrations in the product gas provided insight into the reaction mechanisms.

In this work we significantly redesign the traditional burn tube test by using a small mass of nano-Al/CuO thermite packed into the closed end of a 1.8 m long tube. Upon ignition, a steady luminous front is generated which can propagate part, or all of the way, down the tube. The effect of sample mass and tube radius is investigated. Under certain conditions, the flow velocity can be seen to decrease after some distance, and we use this position to indicate the end of reaction. The quench distance divided by the flow velocity yields a constant value of 3.29 +/- 0.70 ms, which we suggest is the intrinsic burn time for this formulation. The reason material can be seen to flow to such large distances is a result of the reaction time scale being greater than the characteristic momentum relaxation time scale; thus allowing material to flow while it reacts.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
# LLNL-ABS-784878

Recent research has demonstrated thatternary aluminum-boron-iodine (Al-B-I₂) materials prepared by mechanical milling are effective in generating biocidal combustion products. Such reactive materials are of interest for the munitions aimed to defeat stockpiles of biological weapons. In this research, ternary Al-B-I₂ and Mg-B-I₂ composites were synthesized using both one-stage and two-stage milling. One-stage milling consisted of uninterrupted milling of all three components. In two-stage milling, the first stage consisted of a binary B-I₂ powder prepared by mechanical milling, followed by addition of aluminum or magnesiumfor iodine stabilization. Specific compositions for each ternary material were varied.Different milling times were explored to maximize stability of the prepared reactive materials. Stability of the samples wasassessedby their heating in argon at a constant rate using Thermo Gravimetric Analysis (TGA) and observing weight loss. Al-B-I₂ composites with nearly identical properties were prepared by both one and two-staged milling, while two-staged milling for Mg-B-I₂ composites yielded a substantially more stable material compared to the single stage milling. Ternary Mg-B-I₂ composite powder prepared by two-stage milling was also more stable than any of the previously prepared iodine-bearing materials with the same concentration of iodine (20 wt %). Prepared powders were characterized using electron microscopy and x-ray diffraction. Particle size distributions were measured using low-angle laser light scattering. Powders were ignited using Electrostatic Discharge (ESD) and fed into an air-acetylene flame. Burn times and ignition delays were measured optically. This paper will discuss properties of the prepared materials and their correlation with the observed ignition and combustion characteristics.

While aluminum has a long history as a structural reactive fuel, recent studies have shown that the low-level inclusion of various polymers can modify the reactivity and combustion characteristics of these materials. Such polymer inclusions may be interacting or non/weakly-interacting with the aluminum fuel during combustion. Mechanical activation (MA) is an effective means to incorporate these inclusion materials. This process can yield micron-sized, nanostructured composite particles that are fully dense, resulting in altered reactivity due to decreased diffusion length scales and increased interfacial contact area between constituents. While significant studies have shown that MA aluminum-based composites can have similar thermal behavior and reactivity to nanoscale aluminum powder, further efforts are needed to elucidate the ignition and combustion properties of these materials at high temperatures and heating rates.
Several experiments have been proposed and evaluated to characterize ignition properties at high heating rates (e.g., laser ignition; incident/reflected shock ignition; and propellant combustion). However, these materials have not been characterized as a possible reactive structure, such as a casing material in a munition. Small scale experiments have been developed where a structural reactive pellet is dispersed from the detonation of a high explosive driver. The detonation rapidly induces kinetic and thermal energies to the structural reactive in the form of high stresses, pressures, and temperatures. During that process, the heated fuel-rich particles are dispersed into the ambient air, where they are aerobically ignited and burned. The high combustion enthalpy of many metallized fuels can contribute to the work done by the expanding combustion products behind the detonation wave, causing a sustained overpressure and increased thermal loadings (i.e., enhanced blast). The resulting blast can be quantified to characterize the performance of the structural reactive pellet in these small scale experiments.
In this work, several aluminum and aluminum-silicon eutectic alloy based fuels were considered. These fuels were investigated as neat metallic particles (varied particle sizes and morphologies) as well as with either interacting (polytetrafluoroethylene, PTFE) or non/weakly-interacting (low density polyethylene, LDPE) low-level polymer inclusions (varied sizes). Inclusion materials were incorporated via MA, and physical mixtures of the precursors were also investigated in order to ascertain the effect of the MA process. Pressurization rates, high-speed videography, pyrometry, and combustion products were all utilized to draw conclusions on the effects of particle size and morphology as well as the effect between a physical mixture and a mechanically activated mixture using the same precursors. The results of this study were also directly compared to recent detonation ignition investigations of the Ti/2B system.

It is an understatement to say reactive materials are widely used in aerospace and military applications. For example, a space launch vehicle utilizes hundreds of energetic devices (those employing reactive materials) at all phases of its operation including ground support, launch, stage separations, propulsion, and flight termination. Likewise, a cruise missile can use numerous energetic devices for propulsion, flight maneuvering, and payload initiation. In all of the examples, the reliability of the energetic components, which is directly tied to the reliability of the reactive materials, is crucial to the mission&’s success. Manufacturers such as Chemring Energetic Devices design and produce energetic components and systems for specific needs of their customers who are usually the producers of the final systems such as launch vehicles and cruise missiles. The main advantage of energetic devices is its high power-to-weight ratio. The reactive materials&’ rapid rate of energy release allows for compact and lightweight designs that deliver relatively large amount of energy in a very short period of time. Therefore, the reaction characteristics of reactive materials are essential to the functionality of these devices.
While there are numerous formulations and types of reactive materials, studies and development of new materials have been active, especially with the introduction of nano-scale reactive materials two decades ago. However, the transition of the new reactive material technologies from the laboratory to the products has been slower than desired. One of the huddles is the single-point failure nature of the reactive materials in these applications. The heritage materials with many years of pedigree provide the hard reliability data while the new materials do not; and the risks frequently outweigh the benefits. Also the manufacturability is an important factor where the cost of producing devices with new technology must outweigh the risks. Nevertheless, new requirements such as “green” energetics and “insensitive munitions” as well as need for performance enhancement continue to drive the need for novel reactive material technology. And of course, the technology that will drastically reduce the cost of a part is always a manufacture&’s desire and a strong incentive for continued research and development. The goal of this presentation is to provide an overview of energetic devices and the uses of reactive materials, and to present some of the needs and the challenges from an energetic device manufacturer&’s point of view for the purpose of encouraging continued research and development of novel materials.

Mechanically alloyed nanocomposite Almiddot;Mg powders with tailored particle size distributions are prepared and characterized. Compositions of these powders are varied to include 10 to 50 wt % of Mg. The focus of this paper is to study reactions of such powders with water vapor as an oxidizer. Reactions of Almiddot;Mg alloys with water are of interest for a broad range of applications, from underwater propulsion to generation of hydrogen for fuel cells by metal-water reactions. In a set of experiments using a mini-calorimeter, Almiddot;Mg powders are isothermally oxidized at a controlled humidity at several selected temperatures. In complementary experiments, oxidation of these powders in water vapor is studied at controlled heating rates using thermo-gravimetry. In combustion experiments, the powders are fed into the products of an oxygen-hydrogen flame, where they burn in the produced water vapor. Burn times and combustion temperatures of the particles are studied optically. The particle size distribution is directly correlated with the measured distribution of duration of the recorded emission pulses. This correlation enables us to recover the effect of particle sizes on their burn times, and thus determine the burn rates. Results will be compared to recent measurements of burn rates and oxidation kinetics for pure aluminum and magnesium. It is expected that the results will be useful for development of a comprehensive reaction model for the Almiddot;Mg alloys with water vapor.

Aluminum and metal oxide nanoparticles can be combined to form highly energetic systems known as nanothermites or metastable intermolecular composites (MICs). The nanoscales of these materials allow for the rapid release of energy that could valuable in a variety of small scale applications including incorporation into microelectromechanical system (MEMS) devices. As such there is a need for simple, cheap, and effective methods of depositing nanothermites in a small scale and precise manner. Here we report on the use of a 3D printer based system for the patterning of nanothermite inks. This method further allows for the creation of novel experimental systems that allow for the probing of nanothermite reaction mechanism, including the layering of separate Al and CuO nanoparticle thin films.

The surface chemistry associated with the synthesis of energetic nanolaminates controls the formation of the critical interfacial layers that dominate the performances of nanothermites. Indeed the downscaling and control of interfaces offer the opportunity to increase and tune the performances of nanothermites (stability, reactivity and energy release) in the perspective of their integration into MEMS technologies (‘nanoenergetic on a chip&’ applications [1]). Along this line, it has been recently demonstrated that alumina interfacial layers in Al/CuO nanolaminated energetic materials are inevitably formed either through conventional PVD (Physical Vapour Deposition) or TMA (Tetra-Methyl Aluminum)-based ALD (Atomic Layer Deposition) techniques, and that the quality (structure and conformality) of the alumina barrier layer impacts the overall thermal properties of the operating material [2].
Atomic scale simulations then appear as a powerful tool for the characterization of phenomena occurring at the nanoscale to guide the technologists toward the development of advanced nanostructured materials. In this study, DFT calculations are used for the systematic identification and characterization of elementary physical and chemical mechanisms involved in interfacial layer formation. Primary steps of both deposition of copper oxide (CuO) on aluminium surface (Al(111)) and deposition of aluminium on copper oxide surfaces are shown. Chemical reactions such as adsorption, surface migrations, and insertions in subsurface are described thermodynamically and kinetically.[3] These results highlight that asymmetric Al₂O₃-basedinterfaces are formed during technological process: when CuO is deposited on Al(111). interface growth is driven by a competition between massive copper insertion into the subsurface of Al and extraction of aluminium atoms through oxygen adsorption, potentially undergoing a Cu condensation through aluminium oxidation, whereas an amorphization of the CuO (111) surface is observed under Al exposure, with local copper reduction.
[1] C. Rossi, A. Estève, P. Vashishta, J. Phys. Chem. Sol., 71 (2010) 57-58.
[2] J. Kwon, J.M. Ducéré, M. Petrantoni, P. Alphonse, M. Bahrami, J.F. Veyan, C. Tenailleau, A. Estève, C. Rossi, Y.J. Chabal, App. Mat. & Int. 5 (3), (2013) 605.
[3] C. Lanthony, J-M Ducéré, M. Djafari Rouhani, A. Hémeryck, A. Estève, C. Rossi, J. Chem. Phys. 137, (2012) 094707.

Gold-Palladium (AuPd) bimetallic catalyst has attracted many research groups and it is known as the most famous bimetallic Au-based catalyst because of its highly catalytic performance for various reactions. For instance, it is reported that the AuPd bimetallic catalysts are highly active for aerobic alcohol oxidation, hydrogenation of 1,3-cyclooctadiene, direct synthesis of H₂O₂, acetoxylation of ethylene, oxygen reduction in electrodes, and so on. Though novel performance and synthesis method were surveyed well in previous studies, the reasons for such significant performances over AuPd bimetallic catalyst are still unclear.
Herein, in order to clarify the extraordinary catalytic property on AuPd active center, we synthesized AuX (X = Ir, Pt, Pd, Cu, and Ag) supported hydrotalcite catalysts and compared their catalytic performance in the aerobic 1-phenylethanol oxidation, an alcohol oxidation without side/over reactions may help to simplify the discussion.
Various AuX nanoparticles supported hydrotalcite catalysts were prepared by a polyol reduction method using ethylene glycol and polyvinylpyrrolidone as a reducing and a capping agent, respectively. As-prepared AuX-PVP/HT catalysts were characterized by XRD, TEM, STEM-EDS, XPS, XAFS and other analytical methods. In general procedure for the aerobic oxidation of 1-phenylethanol, 4 mmol of alcohol, 5 ml of toluene, and as-prepared Au₆₀X₄₀-PVP/HT catalyst were mixed at under 343 K for 6 h under O₂ flow, and then the products were analyzed by GC-FID.
Yields for the product, acetophenone, were obtained as a following order; AuPd(> 99%) >> AuAg(17.4%) > AuCu(13.8%) > AuPt(7.1%) > AuIr(5.5%). When the electron net charge from X toward Au atoms (the ligand effect of neighbor atom onto Au center) is dominant factor for the reactivity, differences between Au and X in the ionization potential value (one of elucidation factors for electron transfer phenomenon) may lead the way for elucidation of the reactivity. However, the order in ionization potential, Ag > Cu > Pd > Pt >Ir, was not fitted well with the activity. One possible reason is that not only Au but also neighbor atom acts as the active and/or important center for the reaction.
To further study the catalysis over AuPd-PVP/HT which showed the highest activity in the aerobic oxidation of 1-phenylethanol, effect of Au/Pd molecular ratio was investigated. It was observed that with increase of Pd contents till 40% into Au, the yield was drastically increased, thereafter gradual decrease in the yield was monitored in the range of 40-100% Pd content. XPS and XANES analyses indicated that the Au₆₀Pd₄₀-PVP/HT possessed the highest negativity in Au 5d state derived from the charge transfer from neighbor Pd atoms. Ongoing study, we are evaluating the Pd state in AuPd-PVP/HT by XPS and XANES analyses, these will be discussed together for real understanding the catalysis over bimetallic AuPd nano-material

One major challenge in using nanomaterials is how to structure them into a usable form or alternatively how to process them. Nanoparticles and their associated composites must be formulated into mechanically stable structures that nominally implies some type of binder. We demonstrate that electrospray offers the potential opportunity to by-pass traditional casting methods. Multiple components can be employed in both molecular and particulate form. For example we have made mesospheres of Al-CuO-NC where the ratio of the three can be independently controlled. Furthermore there is no limit to additional components that can be added. Other polymers, other nanoparticles, or micron size particles, or even other energetic molecular components can be sprayed, ultimately even materials comprising molecular clusters. The final mesoparticle size can be independently controlled by varying solvent concentration, solvent viscosity, ionic conductivity. Final deposited morphology will depend on solvent vapor pressure and induced evaporation rate. A range of architectures can be achieved. As we have demonstrated nanofibers, mesoparticle and films.

NanoThermite reactions are mechanistically not well understood, due to the ultra-fast transient event and the complexity of probing both the vapor-phase and condensed-state chemistries. In this work we examine the combustion product particles of three nano-sized thermite systems (Al/CuO, Al/WO₃, Al/Bi₂O₃) as a forensic probe of mechanism. Electron Microscopy (EM) and Energy-dispersive X-ray Spectroscopy (EDX) were used to evaluate the combustion product particle size distribution and composition. The results show two distinct product particle size distributions common to all three oxidizers. The larger particles are super-micron (though the precursors were nano-sized) and comprise approximately 90% of the product mass. Simple scaling arguments show that the large population cannot be formed from the vapor given the available residence time. The smaller distribution is sub-100 nm which is primarily the reduced metal formed from vapor phase condensation. This result implies that the majority of the global reaction and thus the energy release is occurring in the condensed phase. Based on these results, a phenomenological mechanism for the nanoaluminum based thermite reaction is proposed.

Nanosized thermite mixtures have been of recent interest due to the observed enhanced kinetics of these systems. While there is a general understanding about the combustion reaction between aluminum and a metal oxide, there is little understanding of why some oxides perform better than others. The tantalum based thermite system was chosen to be studied, due to tantalum having a much higher melting point than that of aluminum, in hopes to develop a greater understanding of thermite systems in general. T-Jump/Time of Flight Mass Spectrometry was used to study the reaction mechanism of tantalum nanopowder reacting with various metal oxides by comparing ignition temperatures with respective oxygen release temperatures. These results were then compared to the aluminum reactions with each respective oxide. Combustion cell analysis was also performed to determine the pressurization rate and optical emission of these reactions.

Reactive materials involving nanoscale components often react through gas-solid processes characterized by large Knudsen numbers. Thus, the heat transfer in the particles, which drives temperature and, thus, temperature-dependent kinetics, cannot be accurately simulated by continuum expressions. Predictive simulation of heat transfer in nanoenergetic systems requires knowledge of the appropriate accommodation coefficients for the gas-solid system. There is considerable evidence that the common approximation of unity thermal accommodation is at least an order of magnitude too large. Some evidence from experimental studies of Altman, and more recently, our group, suggests that thermal accommodation coefficients in metal oxide/air interactions at high temperature are less than 0.01, which suggests that conduction heat losses from nanoenergetic particles are grossly overestimated, and radiative losses underestimated. In addition, the predicted particle temperatures during oxidation will be too low, leading to faster kinetics and transport in real systems. This concept of low thermal accommodation may explain, at least in part, several unexpected observations in nanoscale systems including fast reactivity, high temperatures, and low ignition thresholds. This paper will review the experimental results that suggest low accommodation coefficients are prevalent, will discuss the uncertainty and challenges associated with these measurements, and will speculate on possible implications for nanoenergetic modeling in the limit of very small thermal accommodation coefficient.

The reaction of loosely-packed aluminum / copper oxide (Al / CuO) thermites in a 12 cm long acrylic burn tube was investigated as a function of the fill length from 2 to 10 cm. The velocity of the luminous front was measured both in the filled and unfilled region, and approached 1000 m/s in the unfilled region, independent of the fill length. This value is approximately a factor of two higher than the fastest velocity measured in the filled region, 606 m/s, for the 10 cm filled tube. The velocity increase in the unfilled region is likely due to the increased open porosity, which can support faster flow velocities for a given pressure gradient relative to that in the porous material. A high-speed color imaging pyrometer was used to thermally map the evolution of the flame in both regions. Near the luminous front in the filled section, the temperature was observed to rapidly increase in a 1-2 cm zone to a maximum value near 3200 K, and an average value near 3000 K was sustained in the wake well after the front passes and exits the tube. In partially-filled tubes, even for the lowest fill length of 2 cm, the intermediate and / or product species could be seen to expand forward and completely fill the tube with a sustained temperature of ca. 3000 K. This temperature did not decay during the expansion, suggesting that the material continues to react as it expands. The results raise several questions about what a burn tube experiment is really measuring; such as what fraction of the material has burned when the luminous front passes and what role open cracks or microstructures play in promoting transport. These questions are critically important towards developing a predictive capability for confined, loosely packed deflagrations.

The oxidation during the combustion of metallic nanocomposite materials (MNMs) is a fundamental quantity that dictates various important properties such as sensitivity and reactivity. The size and morphological controlling of MNMs in turn essentially determine the oxidation dynamics. The archetypal MNM is aluminum nanoparticle (Al-NP), which has been studied extensively in the past. However, the oxidation dynamics for aggregated Al-NPs under fast initial heating conditions remain elusive. The key scientific questions are: What is the size dependence on the reaction rate for the oxidation of aggregated Al-NPs, and what are reaction pathways that determine it?
Due to the extremely fine length scale and rapid bursting of the exothermic reaction after the ignition of Al-NPs, experimental research has been a challenge. However, no atomistic simulation capable of describing chemical reactions has been performed to systemically encompass the burning behavior of different sizes of uniformly distributed aggregated Al-NPs (three sets of close-packed Al-NPs, D = 26, 36 and 46 nm, respectively) at time (~2 ns) scales. In order to overcome this computational challenge, we have developed a scalable parallel implementation of reactive molecular dynamics (RMD) simulations.
Here, RMD simulations validated by experimental comparison and quantum molecular dynamics simulations reveal the significance of the agglomeration of Al-NPs and along with the production of small intermediate aluminum-oxide products during the oxidation of aggregated Al-NPs. Comparison of different sets of Al-NPs shows faster reactions of smaller diameter Al-NP aggregates. We find crossovers of the major intermediate products from Al₂O to AlO₂ then to AlO (reaction pathways: Al₂O → AlO₂ → AlO). In addition to the size effect on the reaction rate and reation pathways, also found is the production of the final gas phase product, Al₂O₃, directly from the AlO and AlO₂ intermediates. The simulation suggests an unexpectedly active role of the oxide shell. Such atomistic understanding may pave a way toward rational design for reactive materials as a nanoreactor.

Temperature Jump Time of Flight Mass Spectrometry (T-Jump TOFMS) has previously been used for time resolved speciation of rapidly heated energetic materials. Heating rates of up to ~10⁵ K/s can be attained, which more closely approximates a typical combustion event. One aspect lacking from the current T-Jump TOFMS system is the inability to obtain any information on the energetics of a reaction. Recently developed chip-based micro- and nano-calorimeters are capable of making thermal measurements at a frequency > 100 KHz. We demonstrate the integration of a chip-based nano-calorimeter developed at NIST, within the extraction region of our TOFMS system to enable simultaneous measurement of temporally resolved thermal and speciation data at high heating rates up to ~10⁵ K/s. We apply this approach to analyze the reaction between aluminum and copper in both nanopowder mixtures and thin films. This technique was also used to analyze new thermite based energetic materials synthesized using electrospray synthesis methods.

Traditional studies of nanothermite materials (typically comprised of Aluminum nanoparticles (Al-NPs) with nanoscale metal oxides) involve reacting bulk samples and inferring details of the reaction from this data. The reason for this is that the small scale and fast reactions rates inherent to the materials make it difficult to directly probe the underlying mechanisms of reaction. However, recent advances in dynamic transmission electron microscopy (DTEM) have allowed us to image morphological changes happening between Al-CuO nanoparticles with nanometer and nanosecond resolution. These interactions are found to occur as quickly as 200ns and can take up to 6mu;s to complete. In this work, we compare the materials and morphologies observed directly to the products of bulk reaction. The timescales found experimentally are coupled with discussion of the fundamental timescales of bulk reaction in order to determine the role and nature of a condensed phase nanoscale reaction mechanism on overall reactivity. These concepts are further explored by varying the length scale involved in the bulk reaction by printing layers of Al and CuO into structured thermites and measuring their burn rates.

Recent discoveries on low power Xenon flash ignition of nanoscale aluminum (nAl), carbon nanotubes and mechanically activated Al-PMF composite particles sparked interest on electromagnetically assisted ignition of reactive materials. We mechanically activated microscale particles of Al and Sucrose using ball milling. Bare and soot covered thin thermocouples were used to measure maximum direct thermal heating due to the low-power commercial Xenon flash with a maximum fluence around 1-2 J/cm^2. The particles ignited following the application of the flash and continued combusting and exploding in air through rapid gas generation and Al oxidation.The results show that thermal heating alone is not sufficient and an amplifying effect is necessary to explain ignition, for example through localized surface plasmon resonance (LSPR) theorized for nanoparticles of aluminum (nAl). It is possible that the incorporation of dialectric material through milling enhances LSPR among nanoscale Al lamella that normally occurs due to air gaps in nAl. Such particles sensitive to visual and near-IR radiation can be useful as propellant additives or for hyperthermia to treat cancer.

This study examines the effect of annealing and quenching rate on the stress state of aluminum particles and the flame speed of aluminum and copper oxide composites. Micron-sized aluminum and copper oxide composites were annealed and quenched according to treatments designed to affect aluminum particle mechanical properties. X-ray diffraction (XRD) analysis of the particles reveals the pre-treatment altered the mechanical properties of the aluminum particles. The mixtures were then ignited in a semi-confined tube and flame propagation was measured. Powders were treated to a range of anneal temperatures from 373 to 473 K and quenched according to three different cooling rates. Each treatment affected the stress state of the powder. The change in mechanical properties of the powder is correlated to the flame speed results. An effective heating range for altering flame speed performance was identified as well as the effect of cooling rate on flame speed. Our results show that fast quenching significantly increases flame speeds whereas slow quenching significantly reduces flame speed as compared to the untreated samples. A model is proposed for identifying an optimal treatment for these powders in order to achieve maximum flame speed. These results reveal that altering the mechanical properties of aluminum fuel particles significantly affects their reactivity, particularly when combined with a solid oxidizer.

Spatially propagating reaction waves are central to a variety of energy applications, such as high temperature solid phase or combustion synthesis, and thermopower waves. In this talk, we identify and study a previously unreported property of such waves, specifically that they can generate temperatures far in excess of the adiabatic limit. We show that this superadiabaticity occurs when a reaction wave in either one dimension (1D) or two dimensions (2D) impinges upon an adiabatic boundary under specific reaction and heat transfer conditions. This property is studied analytically and computationally for a series of 1D and 2D example systems, producing an estimate of the upper bound for excess temperature rise as high as 1.8 times the adiabatic limit, translating to temperatures approaching 2000 K for some practical materials. We show that superadiabaticity may enable several new types of energy conversion mechanisms, including thermophotovoltaic wave harvesting, which we analyze for efficiency and power density.

Reactive nanomaterials have become an attractive alternative to conventional explosives. They are defined as systems in which two non-organic solid phases are combined with the potential for being thermally triggered to release chemical energy. For example, Al powders combined with a metal oxide (thermites) have been used for many years for welding and as a pyrotechnic initiator. Among many possible reactive nanomaterials, composite nanolaminates, composed of tens of ultra-thin bilayers of one metal (typically Al) and one metal oxide (such as CuO), are particularly promising and interesting energetic systems because the thickness of each deposited metal and oxide layer can be accurately controlled (from a few nanometers to several hundreds of nanometers). The deposition method makes it possible to obtain uniformly spaced energetic layers with the reactants in intimate contact, and to produce relatively pure material since the deposition is made at low pressure. In this work, DC-magnetron sputtering was used to engineer Al/CuO nano-laminates with controlled thicknesses and interfacial layers. These structures obtained under different deposition conditions were characterized using TEM cross sectional imaging. The layers vary in number and in thickness between 25nm to 500nm. The Cu/O ratio of each CuO layer is also controlled. In all cases the layers have very uniform thicknesses that are separated by atomically resolved interfacial regions. This precise control of the nanostructure allows a quantifiable examination of the relationship between structure and reaction properties. In particular, we show that, by engineering the structural dimensions to the nanometer scale, the reaction propagation flame speeds in such reactive materials can be increased by one order of magnitude compared to similar systems with micron-scale features. We also experimentally explore the role and importance of interfacial layers in such multilayered system. Especially, for bilayer thickness below 200 nm, we demonstrate experimentally that by modifying the chemical nature of interfacial layer, the reaction propagation rates are increased by several orders of magnitude compared to similar systems with naturally formed interfaces. First principles calculations give insight into the interface structure and support our experimental observations. This perspective of tunability along with other attributes such as high volumetric energy density and the capability to produce and manipulate environmentally benign products make reactive nanocomposites very attractive nanoenergetic material systems for wide applications, including environmentally clean primers, detonator, explosives, in situ welding and many others that will be discussed. These materials can be used in conjunction with, or in replacement of traditional explosives, making them the subject of intense current research.

Increasing the heat generated when nanolaminate foils are ignited in air can be accomplished by maximizing the extent of the relatively slow oxidation and nitridization reactions that follow their rapid intermetallic formation reactions. The burning characteristics are dependent primarily upon chemical make-up, and so we have investigated the heat produced by Al/Zr foils where the Al is either commercially pure, or an alloy with Mg, which is of interest because the Mg vaporizes during the reaction. The geometry of the foil also influences the burning characteristics because exposed surfaces cause cooling via radiation, but also heating from reacting with the environment. Therefore, temperature profiles and heats of reaction were measured as a function of foil width and thickness, for both Al:Zr and Al-8Mg:Zr. Temperatures were measured using two-color pyrometry, and heats were measured in a specialized bomb calorimeter.

An understanding of how and when phases form in interfacial reactions is important for the prediction and modeling of reaction initiation and propagation in reactive multilayer foils. Temperature and concentration gradient are two of the most important factors governing phase formation. Thermodynamic and kinetic arguments have been advanced to explain the influence of these factors, but their validity has long gone untested because of an inability to perform sufficiently controlled experiments to test the model assumptions. In particular, in a freely reacting multilayer system the temperature and concentration gradient are linked by the connection between the diffusive mixing rate (which depends on both temperature and concentration gradient) and the heat release rate (which controls the temperature and depends on the mixing rate). This makes it very difficult to study either temperature or concentration gradient independently. We have eliminated this problem by performing experiments using nanocalorimetry, a technique that provides the enhanced temperature control typical of calorimetry but enables heating rates that approach those observed when free-standing multilayer foils react in a self-propagating mode. Using this technique, we have performed a systematic analysis of the phase formation sequence of Al/Ni bilayers over the heating rate range 1000 K/s to 100,000 K/s. The primary output of nanocalorimetry experiments is the reaction enthalpy as a function of temperature. In order to correlate these results with the actual phases formed, we have replicated representative experiments at various heating rates in a time-resolved electron microscope that enables in situ phase identification during the experiment. We will present the conclusions arrived at by the combination of these two techniques.

Exothermic reactions are known to self-propagate in powder compacts, discontinuous laminates, and multilayer foils with rapid releases of heat and light and temperatures ranging from 1000^oC to 3000^oC. Reduction/oxidation reactions often release gases as they travel, and this can lead to particle ejection. Formation reactions typically progress with only condensed phases but they can eject particles as well when their reaction products melt. Further still, propagation can turn unstable at slow velocities, leading to the sequential motion of many reaction bands as opposed to a single, continuous reaction front. In this presentation we explore sources for both unsteady propagation and material ejection during self-sustained exothermic formation reactions in multilayer foils. Multiple experimental observations are shown, drawing on our experimental studies and those of others. These are then linked to numerical studies of unstable propagation and analytical studies of stresses during reaction propagation.

Thermite reactions have been used for over a century in joining applications by using the molten products of the exothermic reaction to braze components together. Using a variety of mechanical methods we fabricate Al:CuO, Al:NiO, and Al:Cu₂O thermite composite foils diluted with excess elemental powder to increase the amount of molten braze material and decrease the amount of gas and particulate ejection. By varying the mass ratio of the constituent powders and the mechanical processing path we then tailor the composite foils to bond aluminum, magnesium, and steel alloys.#8203; The bonding process and properties of the resulting bonds will be described in detail.

The extraordinary sensitivity and extremely small thermal mass of nanocalorimetry sensors allow the study of solid-state reactions in thin films over a broad range of heating rates, from isothermal to 10⁵ K/s. Here, we employ high-temperature nanocalorimetry to study the reaction kinetics of Zr/B and Zr/B₄C reactive multilayers at temperatures up to 1,400K. The effects of heating rate (3,000 to 10,000 K/s) and bilayer period are examined. The microstructural evolution of the multilayers during the reaction is revealed using transmission electron microscopy. We demonstrate that ZrB₂ and ZrB₂/ZrC alloys can be synthesized at moderate temperature using reactive multilayers. The reactions in both types of multilayers proceed in two stages: (1) formation of an amorphous alloy and (2) crystallization of the amorphous alloy. Kinetic parameters for the formation of the amorphous phases and the crystallization processes have been determined.

The most prominent reaction front instability in reactive nanolaminates is the formation of transverse reaction bands. These bands travel in a direction roughly normal to the bulk reaction direction, while their combined width moves the reaction in the bulk direction. The time delay between passage of one band and the subsequent band results in local regions that experience conductive heat flow from the hot reaction product, without the rapid self-heating typical of a stable propagating front. In this presentation, the reaction progression that occurs in these regions is discussed. Using cross-sections that span the gaps between transverse bands from quenched samples, the progression of phase formation was studied using electron microscopy and diffraction techniques. These data, taken from a number of cross-section locations moving serially along the gap in the direction of transverse band travel reveals the time-dependent material changes that occur in unstable reactions. In particular, the high-spatial resolution techniques utilized allow description of the reaction progression at the scale of the reactant periodicity. These results are compared to sections taken from the leading edge of stable reaction fronts. While the high self-heating rate of stable reaction allows rapid formation of the final stoichiometric reaction product, the comparatively low heating rate experienced at the leading edge of the stalled reaction front cause the formation of intermediate phases. These phases are identified and the mechanism creating the resulting instability is discussed.
This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Lawrence Livermore National Laboratory has been recently engaged in the development of custom additive manufacturing techniques. The research has been focused on the refinement of feature size to the micro and nano-scale and broadening of the material sets to include metals, ceramics, polymers, and composites thereof. The methods include electrophoretic deposition (EPD) and direct ink writing (DIW). EPD is a process in which colloidal particles are suspended in a liquid are forced to deposit onto an electrode under an applied electric field. Patterning of the electrode enables complex patterned deposits. DIW is a method which utilizes a computer controlled multi-axis motion stage where and “ink” is deposited onto a substrate. Control of the rheology of the “ink” as it flows through a dispensing nozzle is key to high quality materials. We have utilized both of these methods to elucidate the reaction mechanisms and their relevant length scale in reactive materials. In particular we have investigated thermites and the effect of both primary particle scale, uniformity of mixing, and geometry of reacting structures on the energy propagation rate and mechanisms.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344.

Metal/ Metal Oxide reactions are well known for their high energy content and tunable reaction rate. Mechanistically, the prevalent wisdom is that the micron scale fuel particles react in a homogenous manner whereas at the Nano scale, reactions undertake a condensed phase route owing to sintering on a timescale orders of magnitude shorter than combustion. In this study, we probe the quenched products of thermite reactions for different fuel (Aluminum) sizes to obtain forensic clues to the underlying mechanism. We employed electron microscopy and X-ray spectroscopy to identify the compositions of the quenched products. For the Nano scale reactants, the study revealed the presence of two population distributions formed from separate mechanisms. Furthermore, the larger product species were sliced open using a FIB to provide further insight into the extent of oxidation in the sintered products. Based on these results we advocate the predominance of a condensed phase mechanism which exhibit incomplete oxidation. As a measure to counter early sintering, we also characterize the reaction of custom engineered meso-particles, which are micron sized particles with Nano sized fuel and oxidizer as building blocks with Nitrocellulose as a binder. The nitrocellulose binder in the meso particles would break down into gaseous nitrogen upon heating which disintegrates the particle thus preventing agglomeration. Our results show enhanced reactivity and oxidation of the meso particles compared to the Nano scale reactant mixtures.

Single particle combustion experiments can demonstrate the fundamental reaction mechanisms in energetic systems. In this study, we investigated the ignition of mechanically activated (MA) Ni-Al (1:1 molar ratio) and Al-PTFE (7:3 mass ratio) particles. MA can produce highly reactive materials with nanoscale microstructures, but there are no existing studies on reaction pathways for individual MA particles. Single particles from the MA powders were ignited in air using (a) a hot plate at different temperatures to determine critical ignition temperatures and (b) a CO2 laser to determine critical heating rates and ignition delays for different particles. The reactions were observed using high-speed optical and two-filter infrared imaging with spatial resolutions down to 5 mu;m/pixel to determine ignition delays and maximum ignition temperatures for individual particles. The results show that Al-PTFE particles rapidly ignite and break up due to the decomposition of PTFE beyond a critical heating rate and eject many microscale Al particles that continue to combust in air. Ni-Al particles rapidly react (5-50 ms) in multiple stages that correspond to the melting of Al, Ni and the intermetallic compounds NiAl3 and Ni2Al3.

This work examines the effect of micro/meso structure on the reactivity of composite thermites. Direct ink writing (DIW) is used to print conductive 3D structures which are then used as substrates for electrophoretic deposition of thermite films. The result is a 3D thermite architecture with film thickness, spacing, and geometry as parameters to investigate. We find that the reaction can be described as a rapid multi-phase expansion, producing both particles and gases. The transport properties of the gases and particles can be utilized, along with the known geometry, to determine how neighboring expansion events can interact. If two, or more, expansion waves are allowed to interact, the effective velocity can tailored by either enhancing or retarding energy transport. Furthermore, the mode of energy propagation can be changed from a convective to an advective mode of energy transport depending on the printed microstructure. The results will be used towards the design of more complex 3D reactive structures.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

As a high-density metal, tungsten is of interest for use in penetrators and munitions casings. However, tungsten is not readily ignited, potentially leaving its chemical energy of oxidation unused. In this effort, a set of tungsten-rich composite materials with more than 50 % of tungsten by weight were prepared by mechanical milling. Other component metals include magnesium and zirconium. Substantial powder particle size reduction was observed with either component after short milling times. With magnesium, tungsten remains crystalline and forms increasingly refined composite particles with particle sizes near 30 um, while the addition of zirconium causes tungsten to amorphize. Tests of sensitivity to electric sparks showed that all materials could be reliably ignited with subsequent combustion times of about 100 ms, contrary to unmodified tungsten. Constant-volume aerosol combustion tests showed that as part of the prepared composites, tungsten burns to a substantial degree. Further systematic experiments will be used to establish minimum initiation energies as a function of bulk composition and degree of refinement and amorphization. Net energies that can be recovered by combustion will be determined.

In this presentation we report on a series of reactive oxygen exchange nanolaminates between an oxygen source, CuO, and a reactive metal oxygen sink where the propensity for energy release is tailored by material selection and by multilayer geometry. These results suggest it is possible to create a class of energetic materials whose yield can be tailored for specific applications.
We demonstrate that by considering anion transport in the terminal oxide, we can produce multilayers that are unstable at room temperature, or those which require substantial thermal energy to ignite. We first explored this terminal phase hypothesis by comparing CuO-metal laminates with the reactive metals: Mg, Zr, and Al. Calorimetry analysis is used to measure effective activation energies for each material combination in order to better understand the material property / energy release relationships. By combining the information from calorimetry and equilibrium phase diagrams, we explore how the presence of eutectics in the binary diagrams for both the initial and terminal phases, contribute to the temperature onsets of oxygen exchange.
In addition, we report the use of in situ XPS analysis to explore, with sub nm resolution, the interface chemistry of as deposited nanolaminates precursors to identify the limitations of interface abruptness in the as-prepared state. We find that in all cases CuO|reactive metal interfaces have an unavoidable minimum oxide thickness but this thickness depends on a number of factors including thermodynamic driving force for oxygen exchange, wetting, and oxygen diffusivity.
Finally, we will present results for classic Kirkndall experiments conducted on laminate structures with nanoscopic refractory metal markers at the reactive metal/oxide interface in an attempt to determine the predominant diffusing species at the initial stages of reaction.

Inorganic nano-energetic materials, also known as ‘metastable intermolecular composites&’ (MICs) provide the energetics community with new classes of systems that allow for further tailoring of conventional explosives. In the following work we present our investigation into the thin film thermite class of MICs. Our work shows the energy release trends exhibited by Al/CuO, Zr/CuO, and Mg/CuO multi-layers at slow heating rates of 5k/min via differential scanning calorimetry (DSC). Within this slow heating realm, it was found that the Al/CuO system required the highest temperature values for the exothermic activity to be seen around 700-900°C, while the Zr/CuO samples displayed exothermic activity at the lowest temperatures of 400-500°C, and the Mg/CuO samples exhibited exothermic activity at intermediate temperatures of 500-600°C. This behavior can be explained by the oxidation occurring by a diffusion mechanism that mitigates ion transport by terminal oxide diffusion barrier properties. Therefore the terminal oxide with the highest diffusivity values of Alshy;₂O₃ (D~10^-22cm²/sec) will yield a less thermally active thin film composite. This behavior based on the self- diffusion mechanism has been shown to be the prime avenue energetics operate at slow heating rates. While the diffusion mechanism dominates oxidation behavior at low heating rates, the intricacies of the atomistic transport that occurs still require further investigation. Nano-Kirkendall diffusion experiments were undertaken to determine the prime diffusing species within these laminate structures. Inert diffusion markers (Pt wires) were e-beam deposited via organo-metallic precursors at the oxide/metal interface. Transmission electron microscopy (TEM) analysis was executed before and after annealing steps to discern the dominant diffusing ionic species.

Cyclo trimethylene trinitramine (RDX) is an energetic molecular crystal widely used as explosive in military and civilian applications. Initiation and detonation can be triggered by the plastic deformation of the material. However, very little is known about the mechanics of crystal defects in this material system. In this work we use atomistic simulations to determine the active slip systems in RDX and to rank them in terms of their Peierls stresses. The dislocations with core structures stable in this crystal are identified. The cores contain a type of point defects which are specific to molecular crystals. These are molecules which are rotated, and often distorted, relative to their normal configuration in the crystal. These rotational defects are studied separately from dislocations and their range of stability and energetics are determined. The role of all such defects in the context of initiation is discussed.

The initiation of chemical reactions in solid explosives under impact is primarily driven by the formation and growth of hot spots, wherein extreme plastic deformation and confinement effects can drive local temperatures up by several thousands of degrees. Several factors affect the potency of hot spots such as the exothermicity of the material, the size, geometry and density of the voids, as well as the presence of cracks and grain boundaries. It is known that these hot spots affect both the initial and exothermic chemical events. However, competing viewpoints exist on the origin and relative importance for each of the mechanisms that drive the formation of hot spots, though it is widely accepted that the consumption of energetic material near this local hot spot will transition into a deflagration, explosion or detonation. These violent chemical events occur on extremely short timescales (up to a few 10&’s of picoseconds) and within regions of a few nanometers, making their direct experimental observation challenging. However, these length and time scales are tailor-made for molecular dynamics (MD) simulations. We show with multi-million atom simulations the direct observation of hot spot formation and growth that is a direct consequence of the size and shape of voids in porous RDX crystals. Aspects of non-equilibrium chemistry are discussed within our simulations through careful analysis of the molecular species, their populations, in addition to the vibrational and center of mass temperatures. As a result, we have shown that reactions that are mechanically activated, and in turn form hot spots, are characteristically different from those that result from nominal thermal decomposition. Hot spot growth and quench rates have been measured and provide key insight into the first steps of the shock to deflagration transition in molecular explosives.

Fine thermal actuation by miniature heat sources enables applications from electronics fabrication to tumor cauterization. This work introduces the concept of nanoheaters, i.e. reactive bimetallic material dots (0D), ignited electrically to exothermically release precise heat amounts where and when needed. This concept is extended to nanoheater wires (1D) and foils (2D), as well as bulk nanoheaters (3D) manufactured via ball milling and ultrasonic consolidation of nickel and aluminum powders. The fractal structure of such powders and consolidates, with self-similar, multiscale Apollonian or lamellar packaging, is discovered to hold the key for their controlled ignitability: nanoscale structures ignite first, to produce enough heat and raise the temperature of submicron formations, which then ignite microscale regions and so on; while inert areas quench and arrest the self-propagating exothermic reaction. Therefore, such engineered fractal reactive heaters lend themselves to affordable, high-throughput manufacture; and controllable, safe, efficient, supply-less in-situ thermal release. Various nanoheater geometries, similarities and applications are discussed, with a focus on sputter deposited foils and ball-milled powders in the NiAl system.

Established ignition experiments typically require pressed pellets of energetic materials on the order of 500 milligrams (mg) per sample. Characterization of low-yield novel materials is therefore difficult due to the amount of material needed. A new experiment using a CO₂ laser is proposed that combusts approximately 5 mg of loose powder in each test. A sample consisting of a single layer of particles affixed onto a ceramic plate is ignited by a focused 10.6 mu;m CO₂ laser. A wide range of irradiances, corresponding heating rates, and resultant ignition delays have been examined and quantified by high speed visible photography and infrared thermography. Materials used in this study include common high explosives such as 2,4,6-trinitrotoluene (TNT), 1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX), Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), as well as 2,3-hydroxymethyl-2,3-dinitro-1,4-butanediol tetranitrate (SMX), and some novel energetic co-crystals of the same. The effect of material morphology on ignition and flame structure was studied and compared to pellet ignition experiments. The loose powder density and thickness was also examined and compared to traditional pellets. Preliminary results compared favorably to pellet ignition experiments from literature. Samples of HMX matched with the dual ignition criteria from prior work that depends on surface temperature and total energy transferred. Results for the new novel cocrystals are presented and compared with conventional energetics.

Thermite composites show promise in joining applications as foils that can deliver heat and molten braze to a joint. Preliminary experiments have shown that joint shear strength is related to reactive properties of the foil, which are related to the degrees of microstructural refinement and metal dilution. In this work, we report on an experimental arrangement that allows measurement of reaction temperature, velocity, and mass ejection in Al:NiO, Al:Cu₂O, and Al:Fe₃O₄ foils over an appropriate range of dilutions. Surface characterization techniques are used to identify phases present after the reaction. Trends in the data are reported and discussed.

This study explores microwave heating of TNT mixed with varied morphologies of carbon-based susceptors. Experiments were performed in a microwave exposure chamber and two-dimensional transient temperatures were monitored in-situ microwave exposure using a high speed IR camera. These experiments are coupled with HFSS modeling to understand the influence of morphology on microwave absorption. Results show large temperature gradients when carbon nanotubes (CNT), nano diamond, and carbon nanospheres (CNS) are added to TNT at small concentrations. Smaller temperature changes were recorded with graphene and graphite flakes added to TNT. Video recordings show TNT melting with CNT and nan diamond while CNS showed hot spot formations but did not melt and for both graphene and graphite no heating was observed. Microwave energy absorption is dependent on material properties as well as the shape of the nanoparticles, which affect the magnitudes of the induced electric currents. Experimental results are validated with numerical modeling using Ansys HFSS. Simulations of periodic structures of the carbon-based nanoparticles dispersed in TNT are performed to predict microwave power dissipation and correlate to experimental results.

Pt-Sn surface alloys formed on a Pt(100) substrate are remarkably stable to oxidation - no thermal dissociative adsorption of O₂ occurs under UHV conditions. Nonetheless oxidation of these alloys can be carried out clearly and controllably in UHV by using O₃ (ozone). Ozone is a reactive oxidant, creating high “effective” oxygen pressure in UHV such that large concentrations (up to Q_O = 2.2 and 2.1 ML) of chemisorbed and “oxidic” oxygen were produced on the two ordered c(2x2) and (3rt2xrt2)R45deg Sn/Pt(100) surface alloys, respectively. AES, LEED, HR-XPS, and TPD were used to characterize the oxidized alloy surface, measure the oxygen uptake kinetics, and probe the thermal stability of the oxidized surface. Ozone exposed on the alloy surfaces at 300 K oxidized Sn. Annealing the alloy surfaces during TPD revealed two types of O₂ desorption peaks on each alloy surface: peaks observed at 910 and 1100 K on the c(2x2) Sn/Pt(100) surface alloy are attributed to Pt-O-Sn and Sn-O interactions respectively, and peaks at 750 and 1100 K observed on the (3rt2xrt2)R45deg Sn/Pt(100) surface alloy are attributed to Pt-O and Sn-O interactions. At both surfaces Sn-O interactions lead to the formation of SnO_x at high temperature (> 800 K), which decomposed around 1100 K. SnO_x formed on these surfaces is destabilized by at least 100 K due to the presence of Pt as compared to the oxide formed on a thick layer of Sn on the Pt(100) surface. In contrast, PtO_x on the (3rt2xrt2)R45deg surface is 90 K more stable in the presence of SnO_x on the surface as compared to the oxide formed on the clean Pt(100) surface. Both Sn/Pt(100) surface alloys oxidized more readily than Pt(100), and a c(2x2) Sn overlayer was even more reactive for dissociating ozone.

Nanocomposite thermite powders with nearly stoichiometric compositions, including 2Al-3CuO, 2.35Al-Bi₂O₃, 2Al-Fe₂O_3, and 2Al-MoO₃ were prepared by Arrested Reactive Milling and ignited using Electro Static Discharge (ESD). The powders were placed on a brass substrate as monolayers and as 0.5-mm thick layers. In the former case, individual particles were ejected and ignited; in the latter case, a burning dust cloud formed. Optical emission traces filtered at different wavelengths were recorded to determine characteristic ignition delays and durations of the observed combustion events. Individual particles placed in a monolayer ignited during the ESD while the main emission peak was observed well after the discharge. Powder layers with greater thickness ignited after extended delays. Effect of ignition voltage and spark energy on the observed emission profiles will be discussed. In addition, effect of particle size distribution and effect of surrounding environment on the observed ignition and combustion events will be characterized and discussed for each material.

Nanoscale metastable intermolecular composites, thermites, and intermetallics are energy dense materials that are being explored as alternatives to CHNO-based energetic materials provided their reaction rates can be improved. A reduction in domain size has been found to increase these reaction rates by overcoming mass diffusion limitations. However, as the surface area to volume ratio changes, native oxide layers begin to occupy a significant portion of that volume thus acting as energetic dead weight. Helium droplet mediated cluster deposition is an ultra-high vacuum-based technique that produces cluster matter films from gas-phase atoms and molecules in an oxygen free environment. An introduction to the technique and an overview of our initial studies on magnesium-perfluoropolyether (a pyrolant) and intermetallic Mg-Cu cluster films will be provided. In addition our preliminary efforts to assemble, deposit, and characterize Al-CuO cluster matter films will be presented. DISTRIBUTION A. Approved for public release, distribution unlimited. (96ABW-2013-0244)

Nano-sized metallic powders potentially have many advantages as fuels, including faster, more complete combustion than micron-sized powders. However, the unpassivated nanoparticles of some metals of interest are pyrophoric and highly reactive, making them difficult to handle and include in existing formulations. Nano-scale powders have a much larger surface area that must be passivated to achieve air-stability, compared to conventional powders. Oxide-layer surface passivation of nanoparticle fuels sacrifices a significant portion of energy, presenting one serious drawback in the use of metal nano-particle fuels. Recently, reactive mixed-metal nanopowders produced in sonochemically agitated reactions of TiCl₄ with LiAlH₄ were shown to be exceptionally air-stable without sacrificing energy content. In further work, particles have now been synthesized by also adding LiBH₄ together with the LiAlH₄, thereby incorporation B into the final nanopowder material and further boosting the nanopowder fuel combustion energy content. An aerosolized powder burner is used to investigate the combustion behavior of these particles mixed with gaseous fuels, and quantify the trade-off between energy density and reaction rate when substituting boron for aluminum.

Nanopowders produced by the sonochemical decomposition of a mixed borohydride/tetrahydroaluminate of titanium were annealed to temperatures from 100 °C to 500 °C. The resulting fine black powders were determined to have densities in the 2.2 - 2.6 g/cm³, excellent air stability after anneals above 200 °C, and were found to produce upwards of 33 kJ/g and 83 kJ/cm³ when combusted in an oxygen bomb calorimeter after encapsulation in PMMA. The materials have been characterized by XRD, SEM/EDS and other methods before and after combustion demonstrating the effectiveness of the use of the intermettalic reactive metal nanopowders (RMNPs) to achieve full combustion energy yields. This technology provides combustion energies greater than elemental aluminum while the materials are air stable and formulation tolerant. Highlights of current more applied work transitioning these materials into real world fuels will also be presented.

We have previously demonstrated the the synthesis of highly reactive boron nanomaterials by alkali metal reduction of BCl₃ under sonication, followed by annealing. Unlike ordinary boron powders, these materials combust completely and release close to their theoretical energy content under bomb calorimetry. We have scaled up the synthesis using a commercial (Columbia International CIT-UHiPR-U1000V600) ultrasonic hi-pressure reactor , and measured the combustion properties of the materials by bomb calorimetry, thermogravimetric analysis/differential scanning calorimetry, and aerosolized powder combustion. Standard chemical characterization data will be presented as well.

Boron nitride (BN) is a valuable commercial product. It is a wide band gap semiconductor with high chemical and thermal stability. It has been shown that BN emits in the ultraviolet (UV) range and can be used in UV lasers and light emitting diodes. The chemical and thermal stability of boron nitride make it an effective lubricant at extreme temperatures and its insulative properties make it an effective lubricant when the electrical conductivity of other lubricants would be a problem.
In systems were a gaseous nitrogen source is used melting after reaction results in a diffusion barrier preventing infiltration of the nitrogen to the unreacted boron. This is typically addressed through high degrees of dilution, lowering the flame temperature enough to prevent melting of the condensed phase. This dilution results in low product yield, and therefore requires large batch sizes. Routes using alkali metals to reduce boron oxide have been shown to provide high degrees of conversion when reacted in a nitrogen atmosphere; however, they require several hours of holding time at high temperatures for reaction to occur throughout the compact.
This work seeks to produce hexagonal BN (h-BN) through the reaction of elemental boron with a transition metal nitride. Intimate mixing of the nitride with boron through mechanical activation (MA) eliminates the need for gaseous infiltration for reaction to occur. MA has also been shown to significantly reduce onset temperatures allowing lower ignition temperatures. The need to heat the system is eliminated due to the the high exothermicity of the reactions.
Differential scanning calorimetry with thermogravimetric analysis (DSC-TGA) was used to determine thermodynamic properties. Burn rates and temperatures are reported along with conversion rates for pellet burn experiments. The final products were verified through x-ray diffraction.

Flexible, free standing energetic films have been synthesized and characterized for their combustion behaviors. Aluminum and molybdenum trioxide composites were mixed into a silicon binder and blade cast to form flexible free standing films. This study examines the influence of 0-15% by mass potassium perchlorate additive on the combustion behavior of these energetic films. Varied formulations were explored to ensure the film would not crack during drying, as well as remain flexible and be free standing once dried. All films were cast at a thickness of 1-mm with constant volume percent solids to ensure mixtures cast consistently. The films were ignited in a non-confined test apparatus and flame propagation was recorded with a high speed camera. The results show that as the mass percent potassium perchlorate increased the flame speed of the film decreased. However, if the potassium perchlorate concentration is too low, the film will not self propagate. A difference in the dominant mode of energy propagation coupled with reaction kinetics of this multicomponent system contribute to these nearly paradoxical behaviors. Film energetics is becoming increasingly popular in the research arena because a vairety of technologies are driving a need for localized energy generation in stable, safe and free-standing energetic films.

We investigated the dynamic response of compacted reactive material to shock and blast. Here a powder reactive formulation (Al-Fe₂O₃) was uniaxially cold pressed into a solid cylinder of material and mated to a high-explosive charge of the same diameter. Detonation of the charge transmitted a shock wave to the reactive material and imparted momentum launching it in the direction of the detonation. The material survived launch intact, but deformed dynamically. High-resolution time sequence radiography was used to image the dynamic response in launch. This technique allowed a detailed investigation of material deformation in addition to changes in the internal structure and onset of reactivity. The effect of variations in the initial density of the pressed thermite was also examined. We found that these pressed thermites behave much like solid metals during shock transit, but then respond much differently. Moreover, the material compaction and preparation greatly affects launch and material response.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.