Symposium Organizers
Nicholas Piekiel, U.S. Army Research Laboratory
Steven Son, Purdue University
Karsten Woll, Karlsruhe Institute of Technology (KIT)
Xiaolin Zheng, Stanford University
Symposium Support
Lawrence Livermore National Laboratory
PM02.01: Reactive Laminate I
Session Chairs
Michael Grapes
Karsten Woll
Monday PM, November 27, 2017
Sheraton, 3rd Floor, Hampton
9:00 AM - *PM02.01.01
An Investigation of Several Remaining Unknown Properties of Reactive Multilayers Affecting Ignition and Self-Propagating Reactions
David Adams 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States
Show AbstractReactive multilayers grown by vapor deposition have been developed extensively for advanced joining technology and continue to be explored for other applications such as power sources. Multilayers constructed with a regular, 1-D periodic structure exhibit reproducible ignition and propagating reaction behaviors that make them reliable localized heat sources. As such, these have been utilized for soldering and brazing various, dissimilar temperature-sensitive materials. In addition, reactive multilayers are ideal model systems for fundamental research. Fabricated with precise control of reactant layer thickness and purity, reactive multilayers enable the detailed examination of atomic-scale processes underlying reactant mixing, thermal transport, mass transport and phase evolution subject to high heating rates (~1e6 K/s). With this presentation, we focus on a few remaining unknown properties of these materials that are important to their further development and application. We have utilized advanced characterization methods to better understand the nature of interfacial volumes, thermal transport and compositional variations of different metal-metal multilayers (Al/Pt, Ni(V)/Al and Co/Al) to better understand the complex interplay of design, structure and reactive behaviors. The impact of measured properties is demonstrated by a combined experimental and model-based study of point ignition (involving single pulsed laser irradiation) and transition to steady, self-propagating high temperature reactions. This work was supported by a Sandia Laboratory Directed Research and Development (LDRD) program. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.
9:30 AM - PM02.01.02
Dynamic TEM Characterization of Unsteady ‘Spin-Like’ Propagation of Al-Co Reactive Multilayers
Garth Egan 1 , David Adams 2 , Geoffrey Campbell 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractRather than propagating as a smooth and fast-moving front, certain reactive multilayer films have been observed to undergo unsteady propagation enabled by multiple small fronts that move perpendicularly to the net reaction direction. To better understand this process at the pertinent length and time scales, the Movie-Mode Dynamic Transmission Electron Microscope (MM-DTEM) at Lawrence Livermore National Laboratory (LLNL) was used to study the reaction of Al-Co films with a variety of bilayer thicknesses (25-75 nm). Reaction front speeds were found to vary from 2-6 m/s and produced steady fronts, although slower films did create periodic structures. To produce ‘spin-like’ unsteady propagation, films were pre-reacted to an intermediate state and an in situ cold stage was employed. Both techniques produced similar behavior, with individual transversely traveling bands propagating at 8-12 m/s compared with 0.5 – 2 m/s in the net reaction direction. This work was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering for FWP SCW0974 by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
9:45 AM - PM02.01.03
Shock Compression Initiated Reactions of Nanolaminate Films
Michael Abere 1 , Cole Yarrington 1 , Mark Rodriguez 1 , Paul Kotula 1 , David Adams 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractThe shock-compression response of Ni/Al, Al/Pt, and Ni/AlO nanolaminates has been investigated using a laser launched flyer plate system. The alternating layers of constituent materials were deposited onto a masked sapphire substrate via direct current magnetron sputtering such that the cylindrical flyer diameter (1 mm) was larger than that of the impacted film (0.8 mm). This allowed for the study of the material’s response within the impacted zone as well as post-mortem characterization from within this region with a combination of metrology, X-ray diffraction, and transmission electron microscopy. An impact velocity threshold was determined for each material system, and it was found that this threshold could be tailored either through altering the bilayer thickness or imparting a shear component during impact by using a flyer made of y-cut quartz. These on substrate experiments were then compared to flyer impact ignition results of free standing commercial Ni/Al foils.
Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC. A wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.
10:30 AM - *PM02.01.04
Controlling Multilayered Material Reactivity Using Interface Nanoengineering
Carole Rossi 1
1 , LAAS CNRS, Toulouse France
Show AbstractThere is a recent drive to develop manufacturing methods to create energetic materials on chips. By incorporating nanotechnology in the process, tailored architectures can be produced at scales as low as nanometers, which enables the optimization of ignition and reaction properties. Vapor-deposited reactive multilayers constitute an attractive option because the energetic layers can be deposited directly on chips, as required for novel applications such as micro-actuators, in-situ micro-welds or -soldering, triggering of chemical reactions, and molecular sterilization. Among a large variety of reactive structures, Al/CuO nanolaminates are particularly promising and interesting due to their high thermal output and ability to produce gas, important for functionalities such as micro initiators, MEMS heat sources or exploding foil initiators, just to cite a few. Despite their growing importance for applications, the control of their fabrication/synthesis still lags behind, as fundamental challenges are pushing the engineering and scientific frontiers. For instance, there is little understanding of the formation mechanisms and role of interfaces, let alone methods for controlling their ageing and reactivity.
This talk will review recent methods to substantially stabilize the Al/CuO/Al interface and thus enhance the thermal properties of the nanolaminate film structures. To illustrate the approach taken to investigate such system, two engineered interfaces will be briefly presented and their impact discussed based of recent characterization and modelling: (1) a PVD copper interfacial nanolayer and, (2) an ALD zinc oxide nanolayer, separating the Al from CuO films, with goal of minimizing the formation of interfacial alumina at room temperature.
We demonstrate that the deposition a ZnO nanolayer (~8 nm) on the CuO prior to Al deposition substantially stabilizes the CuO/Al interface and enhances the efficiency of the nanolaminate overall reaction (heat generated). The CuO/ZnO/Al nanolaminates generates 98 % of their theoretical enthalpy within a one-step reaction at 900 °C, in contrast to conventional ZnO-free CuO/Al nanolaminates that produce only 74 % of their theoretical enthalpy, distributed over two distinct reaction steps at 550 and 850 °C. Similarly, sputter-deposition of a pure copper nanolayer (~5 nm) on Al prior to CuO deposition is shown to increase the overall nanolaminate material reactivity. The formation of an Al:Cu alloy with melting temperature lower than pure Al metal is responsible for the enhanced reactivity. This results provides a technological means for stabilizing and controlling the aging of Al/CuO nanolaminates and can be generalized to any Al-based energetic nanolaminates.
These examples illustrate fundamental studies of interface formation and role in energetic nanolaminates are important to develop a mechanistic understanding necessary for the rapid development of applications in this field.
11:00 AM - PM02.01.05
Critical Heat Dissipation Lengths for Gas Suppression in Fully Dense Al:Cu2O:Cu Thermite Foils
Alex Kinsey 1 , Evan Krumheuer 1 , Reza Behrou 1 , James Guest 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractDiluting dense thermites with excess inert metals or oxides is known to reduce the temperature and the velocity of the self-propagating exothermic reactions that can be ignited in these materials. If the amount of dilution is sufficiently high, reaction temperatures can drop below the boiling points of the reactants and products, suppressing metal vapor formation. However, if large thermite-rich regions are present in the microstructure (absent of diluent), significant gas production can occur due to vaporization of the reduced metal in the localized hot spot. Such gas production can lead to material ejection when fully dense foils are used in bonding applications. In this work we prepare fully dense Al:Cu2O:Cu thermite foils using two fabrication strategies: milling the Al and Cu2O thermite powders and adding diluent during the foil fabrication process, and milling all three constituent powders (Al, Cu2O, and Cu) before foil fabrication. Microstructures of the two types of foils and critical heat dissipation lengths are determined via image analysis and compared with finite element heat transfer simulations to explain the suppression of metal vapor in foils produced by milling all three powders together before foil fabrication.
11:15 AM - PM02.01.06
Preparation and Investigation of Silicon Carbide Using Reactive Multilayers of Amorphous Silicon and Carbon
Rolf Grieseler 1 4 , Isabella Gallino 2 , Marcus Hopfeld 1 , Hauke-Lars Honig 1 , Joerg Pezoldt 3 , Peter Schaaf 1
1 Chair of Materials for Electronics, Technische Universität Ilmenau, Ilmenau Germany, 4 Physics Department, Pontificia Universidad Catolica del Perú, Lima Peru, 2 Chair of Metallic Materials, Saarland University, Saarbrücken Germany, 3 Nanotechnology Group, Technische Universität Ilmenau, Ilmenau Germany
Show AbstractReactive metallic multilayer are known for their exothermic phase formation. Commonly, intermetallic phased are formed and the energy is used for e.g. for bonding and soldering 1,2.
Furthermore, other multilayer systems are nowadays used to prepare thin films of different functional materials. A typical example is the formation of MAX phase materials such as Cr2AlC, Ti3SiC2 or Ti2AlC 3–5.
In this paper the preparation of silicon carbide by a reactive multilayer approach is shown. Therefore, amorphous silicon and carbon were deposited on different substrates. It could be shown that the phase formation of the SiC is exothermic. According to literature the formation enthalpy is -74.4 kJ/mol 6. Only few literature can be found on the preparation of SiC using nanoscale precursors. All of this are based on Powders 7,8.
As a first, the formation of 6H-SiC could be shown at 800°C based on ma multilayer system. Insitu XRD measurement at high temperature combined with DTA/DSC measurements provided interesting new insights into the phase formation using a self-propagating high-temperature synthesis route of preparing SiC. The results can open new possibilities of preparing localized electronic devices. Furthermore, the new insights open new routes for the additive manufacturing of high power electronic devices based on SiC.
References:
1. Duckham, A. et al. Reactive nanostructured foil used as a heat source for joining titanium. J. Appl. Phys. 96, 2336–2342 (2004).
2. Woll, K. et al. Ru/Al Multilayers Integrate Maximum Energy Density and Ductility for Reactive Materials. Sci. Rep. 6, 19535 (2016).
3. Grieseler, R., Kups, T., Wilke, M., Hopfeld, M. & Schaaf, P. Formation of Ti2AlN nanolaminate films by multilayer-deposition and subsequent rapid thermal annealing. Mater. Lett. 82, 74–77 (2012).
4. Hopfeld, M., Grieseler, R., Kups, T., Wilke, M. & Schaaf, P. Thin Film Synthesis of Ti3SiC2 by Rapid Thermal Processing of Magnetron-Sputtered Ti-C-Si Multilayer Systems. Adv. Eng. Mater. 15, 269–275 (2013).
5. Tang, C. et al. Synthesis and characterization of Ti2AlC coatings by magnetron sputtering from three elemental targets and ex-situ annealing. Surf. Coatings Technol. 309, 445–455 (2017).
6. Kleykamp, H. Gibbs energy of formation of sic: A contribution to the thermodynamic stability of the modifications. Berichte der Bunsengesellschaft f?r Phys. Chemie 102, 1231–1234 (1998).
7. Yamada, O. Self-propagating high-temperature synthesis of the SiC. 275–279 (1986).
8. Pampuch, R., Lis, J. & Stobierski, L. in Combustion and Plasma Synthesis of High-Temperature Materials (eds. Munir, Z. A. . & Holt, J. B.) 211–218 (Wiley-VCH, 1997).
11:30 AM - *PM02.01.07
Energetic Intermetallic Ni-Al Materials Formed by Cold Spray
Richard Yetter 1
1 Department of Mechanical and Nuclear Engineering, Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractReactive intermetallic nickel (Ni)/aluminum (Al) based compositions were produced by press-consolidation and cold spray manufacture using mixed particles, nickel-clad aluminum or cryomilled Ni/Al material. Samples were analyzed using scanning electron microscopy (SEM) to elucidate particle structure and geometry. The particle size distribution was also measured for both the Ni-clad Al and cryomilled Ni/Al particles. Differential scanning calorimetry (DSC) analysis provided measurement of endothermic and exothermic heat flow associated with various processes occurring during heating, including low-temperature solid-state reactions, melting, and the high-temperature Al/Ni reaction. Laser ignition/reaction propagation measurements were coupled with embedded thermocouples to investigate density and preheating effects on the reaction propagation rate, while homogeneous ignition experiments were conducted to determine ignition temperature and low-temperature heat release. DSC results show heat release for the cryomilled Ni/Al samples initiates at low temperature (approximately 110°C) due to solid-state reaction. No low-temperature solid-state reaction was observed to occur for mixed Ni/Al particles or Ni-clad Al samples until the powders were consolidated. Increased solid-state heat release was observed for cold spray Ni-clad Al and cryomilled Ni/Al samples relative to the press-consolidated samples. Low temperature solid-state heat release decreased with increasing cryomilled Ni/Al helium process gas temperature. Measured ignition delay, preheat temperature, and reaction propagation rate varied with sample orientation, density, and material type. Cold spray consolidated samples (ignited on the final spray layer) exhibited ignition delay times and reaction propagation rates of 12.5 s and 50.1 mm/s for Ni-clad Al and 4.7 ± 0.2 s and 111.5 ± 26.6 mm/s for cryomilled Ni/Al. Ignition delay time increased to 7.6 s and the measured reaction propagation rate reduced to 43.2 mm/s when 200°C helium process gas was used to consolidate the cryomilled Ni/Al. Homogeneous ignition studies indicate thermal runaway occurs for pressed and cold spray consolidated cryomilled Ni/Al samples between approximately 230 and 275°C. Although solid-state heat release was observed to occur for pressed Ni/Al mixed particles and Ni-clad Al, ignition onset occurred around 640 to 650°C. Cold spray formed Niclad Al exhibited ignition onset around 586°C.
PM02.02: Energetic Material Applications
Session Chairs
Monday PM, November 27, 2017
Sheraton, 3rd Floor, Hampton
1:30 PM - *PM02.02.01
Impact Sensitivity and Ignition Mechanisms of Nanoaluminum-poly(perfluorinated methacrylate) Nanocomposites
Lauren Morris 1 , Darla Graff Thompson 2 , Ian Shelburne 3 , Emre Gunduz 4 , Steven Son 4 , Chris Haines 1
1 Armament Research, Development and Engineering Center, U.S. Army RDECOM-ARDEC, Picatinny Arsenal, New Jersey, United States, 2 , Los Alamos National Laboratory, M-7, Los Alamos, New Mexico, United States, 3 School of Aeronautics and Astronautics, Purdue University, West Lafayette, Indiana, United States, 4 School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractNanoenergetic composites are of overwhelming interest to the Department of Defense because of the higher power output and the ability to finely tune the ignition thresholds of these composites. Recently, several variants of a nanoaluminum-poly(perfluorinated methacrylate) (AlFA) have been synthesized and optimized for a variety of applications including reactive warhead liners and bullet spotters. While conventional techniques such as thermal analysis and bomb calorimetry can be used to characterize the reaction mechanism and energy output of AlFA composites, characterizing their dynamic behaviour is more challenging. Bullet spotter applications require a material to be impact sensitive at very low velocities, yet be adequately insensitve. Several live-fire tests were conducted which revealed the AlFA50 material reacted consistently upon target impact at high velocities, but unreliably so at very low velocities. In an effort to better understand the fundamental impact ignition mechanism and to determine the impact velocity threshold of AlFA50 a series of Taylor gas gun experiments were conducted. It was determined that the light-initiation mechanism was consistent with a pinch mechanism, and that the ignition velocity threshold was near 74 m/s. Based on these results, it was hypothesized that the addition of a filler material could be used to sensitize the AlFA50, and that Asay shear impact testing could be used to determine a more optimal shape of such inclusions. Experiments performed using the Asay shear impact test setup confirmed the pinch ignition mechanism, but observations also revealed that the size of the pinch point was important. Finally, it was shown using that the addition of large glass beads (> 1mm in diameter) was effective at sensitizing the AlFA50 material at high and low velocities, with ignition observed at impact velocities as low as 35 m/s.
2:00 PM - PM02.02.02
Ultra-Rapid and Fully Integrated Active Pyrotechnic Safety Switches Integrating Nanothermites
Andrea Nicollet 1 , Samuel Charlot 1 , Vincent Baijot 1 , Alain Estève 1 , Carole Rossi 1
1 , LAAS-CNRS, Toulouse France
Show AbstractTraditional technologies used to manufacture current pyrotechnic switches are based on synthesis, pressing/casting and injection of macroscopic organic energetic materials (explosive or highly energetic materials), which leads to bulky and dangerous systems. We propose, instead, a nanothermite-based safety switch, which provides a compact circuit breaker, ideally suited to protect against overcurrent, external perturbation and short circuit of a broad range of equipments and systems. This new switch is miniaturized based on the integration of a few mg of nanothermites by additive manufacturing methods directly on electronic circuitry. The concept is simple and adaptable to many applications: two printed board circuit (PCB) are bonded together to form a hermetic cavity of 38 mm3 in volume. The bottom PCB contains the electronic circuitry and ignitor element to trigger the switching. A second PCB supports the copper connection as part of the circuitry that must be disconnected. Once ignited, the nanothermite generates the high gas pressure burst sufficient to safely terminate the electrical connections of the circuit in less than 2 ms, well before a short-circuit can occur that could lead to an uncontrolled action, i.e. an accident or catastrophe.
We show that the pressure (up to 1.5 MPa) or force level (up to 50 N) and switching time (from 0.9 to 5 ms) can all be controlled by tailoring the nanothermite composition (type and dimension of oxide particles), stoichiometry and compaction rate, so that the response of the actuator can be tuned. Therefore it can be applied in a broad variety of applications, such as electric storage, aerospace manufacturing (rod and bolt pyrotechnic cutters), human safety, demolition, parachute opening, road vehicles, boats and battery powered machines.
We focus our presentation on the vaporization of a 100 µm-thick copper connection to rapidly disconnect a battery unit (in less than milliseconds) regardless of the magnitude of the fault-current. For example, we demonstrate that varying the compaction rate from 3.3 to 7.1 % of the TMD (Theoretical Maximun Density), the switching time decreases from 3 to 1.5 ms. Tuning the Al/CuO stoichiometric ratio also impacts greatly the switching time. The design, fabrication process as well as switching performances will be presented. The proposed concept is innovative and offers unprecedented advantages: (1) harmless manipulation of products of substances and processes for human; (2) an integrated fabrication framework enabling low cost and mass fabrication, reliability, and nanoscale precision; (3) increased environmental protection: only safe and environmental friendly substances and components can now be chosen and combined to produce the energetic layer; and (4) a versatile design that can be applied to a large number of applications.
2:15 PM - PM02.02.03
Underwater Robotic Welding of Lap Joints with Sandwiched Reactive Multilayers—Thermal, Mechanical and Material Analysis
Aseel Hussien 1 , Abdelaziz Al Zaabi 1 , Ayesha AlKhoori 1 , Cesare Stefanini 1 , Federico Renda 1 , Syed Jaffar 1 , Ibrahim Gunduz 2 , Kyriaki Polychronopoulou 1 , Claus Rebholz 3 , Charalabos Doumanidis 1
1 , Khalifa University, Abu Dhabi United Arab Emirates, 2 Department of Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 3 Department of Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia Cyprus
Show AbstractUnderwater welding using reactive materials pre-deposited at the junction surfaces as a self-contained, in-situ ignitable heat source mitigates external power and gas supply requirements, lending itself to robotic implementation eliminating the cost along with health and safety hazards of human welder-divers. As such it has received recent attention for construction of large marine infrastructure such as offshore oil and gas platforms, subsurface pipelines for coastal rapid transportation modes (e.g. Hyperloop), artificial island and port structures, along with ship and submarine repair and maintenance without dry docking. This project reports on lap joining of aluminum sheets with sandwiched commercial reactive Ni-Al multilayers, perforated with orthogonal, isometric and Apollonian opening patterns to allow for melt fusion under compression upon ignition, in saline and deionized water as well as air for comparison.
Finite-element thermal simulations are employed to study the resulting welding temperature field and melt conditions, and to optimize the reactive multilayer geometry and requisite thickness. Optimally designed such joints are thermally ignited in a series of underwater and dry experiments under compression and monitoring via infrared pyrometry and thermocouple measurements of the surface temperature field during welding validating computational simulations. The lap joints are subjected to standard shear testing, and comparable compliance, strength and toughness values of the welds are assessed for underwater and dry joints. Scanning electron (SEM) and optical microscopy of the weld sections reveal rapidly melting and solidifying microstructures of the parent metal, with minimal melt flow and perfusion of nickel aluminide aggregates from the reacted multilayers, and no signs of cavitation. X-ray microanalysis (EDX) and diffraction (XRD) spectra reveal limited oxide and chloride presence in joints under underwater saline conditions relative to those in air. Potential longer-term corrosion and hydrogen embrittlement effects are under study. Last, implementation feasibility of metal jointing with sandwiched multilayers for underwater additive manufacture is demonstrated in-place by a custom-designed remotely operated vehicle (ROV) robot in test pool.
2:30 PM - PM02.02.04
Combustion Joining of Regolith Tiles for the In Situ Fabrication of Launch/Landing Pads on the Moon and Mars
Robert Ferguson 1 , James Mantovani 2 , Evgeny Shafirovich 1
1 , The University of Texas at El Paso, El Paso, Texas, United States, 2 Granular Mechanics and Regolith Operations Lab, Kennedy Space Center, Kennedy Space Center, Florida, United States
Show AbstractTo mitigate dust problems during launch/landing operations in lunar and Mars missions, it is desired to build solid pads on the surface. Recently, strong tiles have been fabricated from lunar regilith simulants using high-temperature sintering. The present work investigates combustion joining of these tiles through the use of exothermic reactions. Based on thermodynamic calculations, it is hypothesized that combustion of a stoichiometric nickel/aluminum mixture in the gap between the tiles will weld the regolith tiles together. The objective is to experimentally determine the minimum distance between two regolith tiles that is needed for the formation of a strong weld through a self-propagating combustion of the intermetallic mixture. The mixture, placed in the gap between tiles fabricated from JSC-1A lunar regolith simulant, is ignited by a CO2 laser in an argon environment. The combustion front propagation over the mixture is studied using video recording.
2:45 PM - PM02.02.05
Metal Fuels as Recyclable, Zero-Carbon Energy Carriers
Philippe Julien 1 , Jeffrey Bergthorson 1
1 , McGill University, Montreal, Quebec, Canada
Show AbstractThe global energy share of clean, renewable electricity, produced through wind, solar, or hydro technologies, keeps increasing and its cost is now starting to become competitive with electricity produced by fossil fuels. However, to keep increasing this share, and to fully replace fossil fuels, it is imperative to develop a convenient, energy dense, and transportable form of energy carrier. Energy storage is essential not only for portable applications such as cars and ships, but also to compensate for the intermittent nature of these alternative energy sources. So far, the two proposed solutions, batteries and hydrogen, have failed to become serious alternatives to fossil fuels and are confined to specific markets. Batteries are expensive, have low energy densities, and can only store small quantities of energy for short periods of time. Hydrogen also has a low energy density, but also presents high risks of accidental and intentional explosions.
Our research group proposes to make use of metal powders to store and transport large quantities of clean and renewable electricity. Metal fuels are produced from metal oxides with clean energy, either directly with electrolysis or by reducing the metal, such as iron, with hydrogen. Upon utilization, the only products left are metal oxides, which can be collected and reprocessed back into metal fuel, thus closing the materials loop and fuel cycle, eliminating waste.
Two different methods exist for converting metal fuels into a useable form of energy. The first option is to burn the metal fuel to release heat, which can be used directly or can be converted into mechanical motion or electricity using external-combustion heat engines (Rankine or Stirling).
The second option is to react the metal fuel with water at high temperatures and pressures to produce heat, steam, and hydrogen. The hydrogen can be used with a fuel cell to make electricity, or can be directly burnt in an gas-turbine engine or a reciprocating engine to produce mechanical motion or electricity.
This talk provides an overview of the metal-fuel concept, introduces potential candidates for metal fuels and their potential “green” production methods, along with different concepts of technologies for the utilisation of those fuels. The present work will also provide different application scenarios that could be implemented in the short term and in the long run.
PM02.03: Insights on Ignition from Atomistic Simulations
Session Chairs
Monday PM, November 27, 2017
Sheraton, 3rd Floor, Hampton
3:30 PM - *PM02.03.01
Chemical Bond Breaking Initiations of Reactive Materials under Thermomechanical Extremes by Nonequilibrium Reaction Dynamic Simulations at the Quantum Solid-State Chemistry Theory Level
Anguang Hu 1
1 , Defence Research and Development Canada, Medicine Hat, Alberta, Canada
Show AbstractIn chemical reaction initiations of reactive materials under thermomechanical conditions, where rapid adiabatic compression and expansion are the rules in general, chemical bond breaking processes too fast to reach the equilibrium of the system. Consequently, such chemical reaction initiations can depart radically from their equilibrium contents. It means that all probabilities of finding the system in conformer, energy and motion mode spaces do not follow statistical laws. The purpose of this presentation is to evaluate nonequilibrium chemical reaction initiations of reactive materials under thermomechanical conditions using nonequilibrium reaction dynamic simulations at the quantum solid-state chemistry theory level. In these simulations, quantum solid-state chemistry calculations under thermomechanical conditions will provide reaction dynamics in terms of structural conformer and reaction mode spaces, and energy, enthalpy, thermal heat and mechanical stresses within theses conformer and reaction mode spaces. The thermal heat is approximately expressed as the energy at the terminal point of reaction coordinate change of the oscillation, resulting in a reaction quasi-temperature based on the force constant. The free energy function from the Landau phase transition theory establishes clear correlations between changes in chemical bonding, energy, enthalpy, thermal heat and mechanical stresses when a chemical bond-breaking reaction is initiated in reactive materials under thermomechanical extremes. Simulations show that under thermomechanical conditions the fluid-like state in reactive materials can be generated when the coupling of mechanical work with thermal heat occurs, leading to an ultrafast reaction initiation. Thus, it may be that the initiation of reactive materials may be determined by their chemical bonding and mechanical properties associated with the coupling between mechanical work and thermal heat in the response to thermomechanical extremes.
4:00 PM - PM02.03.02
Solid-State Interdiffusion, Phase Nucleation and Growth Mechanisms in Ni/Al Nanolaminates by Atomistic Simulations
Christian Brandl 1
1 , Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen Germany
Show AbstractAlthough Ni/Al nanolaminates are the prototypical system for self-propagating reacting system, the phase selection and the detailed phase transformation pathways in the solid-state reaction during ignition are still elusive.
Using molecular dynamics simulations with a semi-empirical interatomic potential for the Ni-Al system, relatively long-time scale diffusion (3 µs) and phase nucleation is studied under isothermal conditions between 750 K and 900 K below the melting temperature of Al. The detailed spatiotemporal analysis of the diffusion mechanisms and the B2-NiAl nucleus growth reveals interface diffusion to enable required asymmetric Ni mass transport at lower temperatures. At higher temperatures, the Al(+Ni) interdiffused solid-solution crystal melts and Ni mass transport for B2-NiAl crystals occurs through diffusion through the liquid, which is abruptly interrupted by the formation of complete B2-NiAl interdiffusion layer.
The temperature dependent nucleation and growth kinetics are analysed in the context the prevailing mesoscale models for phase nucleation and discussed in context of classical nucleation theory with and without concentration gradient.
The influence of the initial microstructure in the Al and Ni layers are investigated by including an epitaxial incoherent growth twin boundary. The resulting B2-NiAl morphology and kinetic signatures are compared to previous “single” crystal processes. The observed mechanistic and kinetic differences are discussed in context of subcritical annealing experiments with different initial microstructures.
4:15 PM - PM02.03.03
A Molecular Simulation Study of Intermetallic Nucleation at Ni/Al Interfaces in Multilayer Films
Peng Yi 1 , Michael Falk 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractThe ability to tune and control the ignition of reactive materials for a broad range of application conditions relies on a fundamental understanding of the early stage reaction mechanisms in these materials. As an example of this basic understanding, DSC and TEM experiments in the Ni/Al multilayer system have suggested that the formation of intermetallic phases can be suppressed by a high heating rate, giving other intermetallic phases an opportunity to form instead. Given that different heating rates lead to different composition gradient across the interface, at a given temperature, the suppression is thought to occur because the composition gradient affects both the thermodynamics and the kinetics of the nucleation of intermetallic phases.
We used molecular dynamics simulations to study the nucleation of the non-stoichiometric intermetallic compound, NiAl (B2), in the Ni/Al multilayer system, focusing on how composition gradients at the Ni/Al interfaces impact nucleation of the B2 phase.[1] Both high (>1500K) and low (<750K) temperature ranges were investigated, where reaction occurs in the liquid and solid states, respectively. Simulations were designed to study nucleation within a constant composition gradient under isothermal conditions. We observe that nucleation is inhibited by the presence of a composition gradient in both temperature ranges. The effect of the composition gradient on the thermodynamic driving force for nucleation is formulated using Desré and Yavari’s modification of classical nucleation theory [2]. We then present a hypothesis for altering reaction paths in the case where multiple reaction products can form during nucleation at an interface, and the impact on ignition within applications is discussed.
1. Yi, P., M.L. Falk, and T.P. Weihs, Suppression of homogeneous crystal nucleation of the NiAl intermetallic by a composition gradient: A molecular dynamics study. The Journal of Chemical Physics, 2017. 146(18): p. 184501.
2. Desré, P.J. and A.R. Yavari, Suppression of crystal nucleation in amorphous layers with sharp concentration gradients. Physical Review Letters, 1990. 64(13): p. 1533-1536.
Symposium Organizers
Nicholas Piekiel, U.S. Army Research Laboratory
Steven Son, Purdue University
Karsten Woll, Karlsruhe Institute of Technology (KIT)
Xiaolin Zheng, Stanford University
Symposium Support
Lawrence Livermore National Laboratory
PM02.04: Powder Combustion of Metal and Alloys I
Session Chairs
Tuesday AM, November 28, 2017
Sheraton, 3rd Floor, Hampton
9:00 AM - *PM02.04.01
Replacing the Alumina Shell on Aluminum Particles with an Energetic Salt
Michelle Pantoya 1 , Dylan Smith 1
1 , Texas Tech University, Lubbock, Texas, United States
Show AbstractThe kinetics of aluminum energetic mixtures are shown to approach those of organic molecular explosives by replacing the Al2O3 passivation layer with Aluminum Iodate Hexahydrate (AIH), an energetic salt. Because AIH is a salt, the energy released by AIH is significantly less than the energy released from the formation of Al2O3 form unoxidized Al. The Al3+ in AIH is a strong Lewis acid facilitating increased reaction rates with flame speeds as high as 3200m/s. A combination of 80nm Al particles and replacement of the Al2O3 passivation shell result in reaction kinetics from Al mixtures similar to those of organic molecular explosives. Flame speed measurements are used to show that reaction rates in AIH mixtures are determined by AIH/Al2O3 ratio, oxygen balance (OB), and density. Tailoring the AIH/Al2O3 ratio, OB, and density to optimize reaction rate will result in further increases in reaction rates from Al energetic materials than have already been achieved with AIH mixtures (3200m/s).
9:30 AM - PM02.04.02
Improved Energetic-Behaviors of Spontaneously Surface-Mediated Al Particles
Kyung Tae Kim 1 , Dong Won Kim 1 , Soo Hyung Kim 2
1 , Korea Institute of Materials Science, Changwon Korea (the Republic of), 2 , Pusan National University, Busan Korea (the Republic of)
Show AbstractSurface-mediated Al particles are synthesized by incorporating the stable fluoride reaction of Al-F on a pure Al surface in place of natural oxides. Al particles with fluoro-polymer directly adsorbed on the surface show a considerable capability to overcome limitations caused by the surface oxide. Here, we report that Al fluoride when spontaneously formed at the poly(vinylidene fluoride)/Al interface serves as an oxidation-protecting layer while also providing an efficient combustion path along which the internal Al rapidly reacts with external oxygen atoms. Both thermal oxidation and explosion tests of the poly(vinylidene fluoride)/Al particles show superior exothermic enthalpy energy and simultaneously rapid oxidation reactivity compared to those of Al2O3 passivated Al particles. It is clearly elucidated that the enhanced energetic properties of Al particles mediated by poly(vinylidene fluoride) originate from the extraordinary pyrolytic process of Al fluoride occurring at a low temperature compared to Al2O3 passivated Al. Hence, these results clarify that the surface mediation of Al particles can be significantly considered as advanced technology for many energetic applications.
9:45 AM - PM02.04.03
Facile Thermal and Optical Ignition of Silicon Nanoparticles and Micron Particles
Sidi Huang 1 , Venkata Sharat Parimi 2 , Sili Deng 1 , Srilakshmi Lingamneni 1 , Xiaolin Zheng 1
1 , Stanford University, Stanford, California, United States, 2 , Applied Materials, Santa Clara, California, United States
Show AbstractSilicon (Si) particles are widely utilized as high-capacity electrodes for Li-ion batteries, elements for thermoelectric devices, agents for bio-imaging and therapy, and many other applications. However, Si particles can ignite and burn in air at elevated temperatures or under intense illumination. This poses potential safety hazards when handling, storing, and utilizing these particles for those applications. In order to avoid the problem of accidental ignition, it is critical to quantify the ignition properties of Si particles as functions of their sizes and porosities. To do so, we first used differential scanning calorimetry to experimentally determine the reaction onset temperature of Si particles under slow heating rates (~20 K/min). We found that the reaction onset temperature of Si particles increased with the particle diameter from 805°C at 20-30 nm to 935°C at 1-5 µm. Then, we used a xenon (Xe) flash lamp to ignite Si particles under fast heating rates (~103 to 106 K/s) and measured the minimum ignition radiant fluence (i.e., the radiant energy per unit surface area of Si particle beds required for ignition). We found that the measured minimum ignition radiant fluence decreased with decreasing Si particle size. Additionally, it was most sensitive to the porosity of Si particles. These trends for the Xe flash ignition experiments were also confirmed by our 1-D unsteady simulation to model the heat transfer process. The quantitative information on Si particle ignition included in this manuscript will guide the safe handling, storage, and utilization Si particles for diverse applications, and prevent unwanted fire hazards.
10:30 AM - *PM02.04.04
Reactivity of Aluminum/fluoropolymer Based Composite Materials in Response to Explosive Shock Initiation
Christopher Crouse 1
1 Munitions Directorate, Air Force Research Laboratory (AFRL), Eglin AFB, Florida, United States
Show AbstractA cylinder expansion (CYLEX) test series was performed to investigate the reactivity of aluminized fluorinated acrylate (AlFA) nanocomposite materials when initiated by the shock from an explosive donor. AlFA is a thermoplastic composite comprised of aluminum nanoparticles chemically integrated into a fluorinated polymethacrylate matrix. The high reactivity of this novel material is a result of the oxidizer (fluorine contained within the polymeric matrix) being integrated into the composite material and bonded intimately to the aluminum fuel. Prior observation of the reactive performance of these composites has been investigated through multiple tests including open air pellet burns, instrumented tube burns, high strain rate impact studies, as well as constant volume explosive blast studies. The current CYLEX series utilized an annular ring of the AlFA composite material confined within a copper cylinder and driven with an explosive donor charge in the center. The wall velocity of the copper cylinder was monitored with respect to time. The composition of the annular ring was varied throughout the test series and observed changes in the wall velocities were able to be attributed to compositional changes in the annular composite materials. Experimental results suggest the composite AlFA material is capable of reacting on the microsecond timescale. An overview of previously collected performance data will be presented in addition to current experimental results from the CYLEX testing.
11:00 AM - PM02.04.05
The Effects of Particle Size and Chemistry on Explosively Launched Combustion of Al-Mg-Zr Composite Powders
Timothy Weihs 1 , Elliot Wainwright 1 , Shashank Vummidi Lakshman 1 , Demitrios Stamatis 2 , Forrest Svingala 2 , Rebecca Wilson 2 , Amber Knott 2 , Robert Brothers 2 , Jim Lightstone 2
1 , Johns Hopkins University, Baltimore, Maryland, United States, 2 EOD Tech Division, NSWC Indian Head, Indian Head, Virginia, United States
Show AbstractTo improve the combustion performance of metal fuel powders researchers often vary the size, chemistry, or coating of the powders. Here we describe the combustion performance of Al-Mg-Zr powders that are being developed to provide easy ignition and long, complete burns for bio-agent defeat applications. The powders are prepared by ball-milling Al, Al-Mg, and Zr powders to form composite powders with fine Zr inclusions in an Al-Mg matrix. Upon ignition, the Al and Zr intermix and form compounds exothermically, rapidly heating the particles to temperatures where high-efficiency combustion can occur. The refinement of the Zr inclusions is tuned to lower ignition thresholds below 500oC, and the size and chemistry of the powders are varied to optimize combustion properties, such as the duration, temperature, and degree of oxidation. In the present study Al-Mg-Zr powders are explosively launched in a closed, air-filled chamber without oxidizer powders. The resulting temperature, pressure, and reaction products are characterized as a function of time, and high-speed videos of the combustion process are captured. Four different sizes of 4(Al-8Mg):Zr powders (0-10micron, 10-32micron, 32-53micron, and 53-75micron) and three different Al-Mg-Zr compositions with similar size distributions ((Al-8Mg):3Zr, (Al-8Mg):Zr, and 4(Al-8Mg):Zr, all <75micron) are investigated. Their combustion behavior is shown to be superior to that of the much smaller Valimet H-2 (3.5micron) Al, with more rapid ignition, higher temperatures and pressures, and more complete combustion, even without a secondary oxidizer. Measured combustion properties are compared to model predictions, and vidoes from vented chamber tests will be shown to highlight differences between these large Al-Mg-Zr composite powders and the smaller Valimet H-2 Al powders. Some of the Al-Mg-Zr powders are also coated with an iodine containing polymer, prior to testing, to assess the impact of the coating on combustion efficiency and iodine release.
11:15 AM - PM02.04.06
Boron-Metal Fluoride Reactive Composites.
Siva Kumar Valluri 1 , Mirko Schoenitz 1 , Edward Dreizin 1
1 , New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractThere has been substantial interest in improving boron’s ignition and combustion because of its high energy density and hence potential as a fuel in propellants and explosives. The naturally occurring oxide layer on the particles, which sometimes exists as a hydroxide, is the primary cause of the boron extended ignition delays. Further, the full-fledged combustion of boron particles is rate limited by relatively slow heterogeneous surface reactions. Using boron with oxidizers containing fluorine may accelerate both its ignition and combustion processes. Formation of oxyfluorides, stable as gases at combustion temperatures can also reduce the generation of condensed combustion products undesirable for most applications. In this work, fluorine based oxidizers cobalt (II) fluoride and bismuth (III) fluoride were mechanically milled with boron to produce reactive composites. With 50 wt. % of boron, the composites were fuel-rich, comprising 1 – 100 µm particles with nanosized oxidizer fragments mixed into agglomerates formed by nano-sized primary boron particles. Thermo-analytical measurements in inert gas showed a mass loss of ca. 20% at around 450 °C, which is consistent with the loss of boron trifluoride as a gas. X-ray diffraction analysis supports this observation because the expended samples show the weakening of boron peaks and loss of metal fluoride peaks leaving behind just the metals in the starting metal fluorides, i.e., cobalt and bismuth. The ignition temperatures of both the composite powders coated on an electrically heated filament were found to be unusually low, around 350 °C. The prepared composites were also initiated by an electrostatic discharge (ESD). The samples placed in 0.5-thick powder layers could not be ignited even at the highest ESD energy available, 4 J. However, minute quantities of powders placed on a tip of a needle could be ignited and their spectrographic yields were measured. A combination of a low ESD sensitivity and low ignition temperatures may be very attractive for a range of applications. The paper will further discuss combustion experiments with the prepared materials ignited by passing individual powder particles through a laser beam.
11:30 AM - PM02.04.07
Evolution of Composite Microstructure During Ball Milling and Its Effects on Ignition
Shashank Vummidi Lakshman 1 , John Gibbins 1 , Elliot Wainwright 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractA popular method of improving the energy density of propellants, pyrotechnics, and explosives involves the incorporation of aluminum in their formulations. However, the ignition temperature dependence of aluminum on its particle size and poor combustion efficiency, due to agglomeration and oxide cap formation, has limited its use. Next-generation composite Al-Mg-Zr fuels developed for bio-agent defeat applications rely on intermetallic formation reactions to rapidly heat the particles to temperatures where high-efficiency combustion can occur. These composite particles, synthesized by ball milling, have Zr inclusions in an Al-Mg matrix. Based on the milling parameters, not only does the overall powder size distribution and morphology change, but also the inclusion size and its distribution in the matrix. In the presented work, we discuss the effect of milling parameters on four different Al-Mg-Zr compositions ((Al-8Mg):3Zr, (Al-8Mg):Zr, 3(Al-8Mg):Zr and 4(Al-8Mg):Zr), milled for five different times (30, 45, 60, 75 and 90 min). We use Matlab to analyze cross-sectional SEM images of the powder compacts to calculate Zr inclusion size distributions. For a fixed ball to powder ratio (BPR), we observe finer Zr inclusions and a more uniform dispersion of the inclusions in the Al-Mg matrix as milling time increases. To illustrate the effect of microstructural refinement on ignition, we used a heated filament setup to measure the ignition temperature of these powder compacts. As an example, in the case of 3(Al-8Mg):Zr powders, we observe a decrease in ignition temperature from 800 K to 730 K with an increase in milling time. Whereas for (Al-8Mg):Zr powders, we observe an initial decrease i.e. 750 K to 650 K, with increased milling time, but with further refinement, the ignition temperature rises due to intermixing of the reactants.
11:45 AM - PM02.04.08
Combustion of Magnesium Particles in Different Oxidizing Environments
Xinhang Liu 1 , Mirko Schoenitz 1 , Edward Dreizin 1
1 , New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractMagnesium is a popular metal additive used for propellants, explosives and pyrotechnics. It is expected to burn primarily in the vapor phase; however, it generates rapidly condensing oxide particles as products. The rate of condensation and locations where the condensed MgO particles are formed define the temperature gradients around burning Mg particles, and thus affect their burn rates. Transport of vapor and condensed combustion products depends strongly on the surrounding flow conditions; these processes are also affected by the type of oxidizing environment. Presence of carbon oxides and steam may promote heterogeneous reactions on surface of burning magnesium particles, which affect both the bulk burn rates and combustion products. The effects of flow conditions were recently characterized for magnesium burning in combustion products of an air-acetylene flame. This work expands the range of oxidizing environments and includes different flow conditions in an attempt to develop a mechanistic model of combustion for magnesium. Experiments were performed with magnesium particles burning in air and in a hydrogen-oxygen flame. In air, both laminar and turbulent flow conditions are achieved, whereas only laminar flows exist in the products of the hydrogen-oxygen flame. In air, particles are ignited by passing through a laser beam. In hydrogen-oxygen flame, the particles ignite while traveling through the flame. Following the previous work, particle size distributions are correlated with the measured distribution of the burn time durations to obtain the effect of particle size on its burn time. The correlations are obtained for different environments and different flow conditions. Experiments use a spherical magnesium powder with the nominal particle sizes of 1-11 μm. In hydrogen oxygen flames, the particles are introduced by a carrier gas. Both argon and nitrogen are used to elucidate the effect of nitrogen on combustion of magnesium. Two IR photomultipliers equipped with interference filters at 700 and 800 nm are set to record the light emission during the combustion experiment. In addition, a 32-channel photosensor coupled with a visible light spectrometer is used to record time resolved spectra of the burning particles. Burn times are obtained from the emission pulses produced by individual burning particles. Combustion temperatures are calculated assuming that the burning particles behave as gray bodies. The combustion products are collected and examined by SEM in order to observe the changes in their morphology and composition during combustion. This talk will discuss results of magnesium particle combustion experiments in different environments and focus on interpreting these results and on developing a mechanistic understanding of the magnesium combustion process.
PM02.05: Insights on Ignition from Experiment
Session Chairs
Tuesday PM, November 28, 2017
Sheraton, 3rd Floor, Hampton
1:30 PM - *PM02.05.01
Laser Initiation of Photothermally Active Metal-Ligand Charge Transfer Complexes
Katie Brown 1 , Chris Snyder 1 , Steve Clarke 1
1 , Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractExplosive metal-ligand charge transfer (MLCT) complexes have been synthesized and characterized at Los Alamos National Laboratory. These materials have been shown to have significantly lower sensitivity to traditional stimuli, including impact and friction, as compared to common primary explosives historically used in detonators. Owing to their broad absorption over the visible and near-infrared, these explosive MLCT complexes can be photothermally initiated with laser light from common benchtop sources. The ensuing deflagration can prompt a detonation in PETN or other detonator materials, making our photoactive explosives candidates for laser detonator material. Efforts to optimize the detonation of PETN via laser initiation of our photoactive explosives are described here.
2:00 PM - PM02.05.02
Electroless Deposition and Ignition Properties of Si/Fe2O3 Core/Shell Nanothermites
Sili Deng 1 , Sidi Huang 1 , Yue Jiang 2 , Jiheng Zhao 1 , Xiaolin Zheng 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractThermite, a composite of metal and metal oxide, finds wide applications in power and thermal generation systems that require high energy density. Most thermite research has focused on using aluminum (Al) particles as the fuel. However, Al particles are sensitive to electrostatic discharge, friction, and mechanical impact, imposing a challenge for the safe handling and storage of Al-based thermites. Silicon (Si) is another attractive fuel for thermites due to its high energy content, thin native oxide layer, and facile surface functionality. Several studies showed that the combustion properties of Si-based thermites are comparable to those of Al-based thermites. However, little is known about the ignition properties of Si-based thermites. In this work, we determined the reaction onset temperatures of mechanically mixed Si/Fe2O3 nanothermites and Si/Fe2O3 core/shell nanothermites using differential scanning calorimetry. The Si/Fe2O3 core/shell nanothermites were prepared by an electroless deposition method. We found that the Si/Fe2O3 core/shell nanoparticles had a lower reaction onset temperature (~550°C) than that of the mechanically mixed Si/Fe2O3 nanothermites (>650°C). The onset temperature of the Si/Fe2O3 core/shell nanothermites is also insensitive to the size of the Si core nanoparticle. Those results indicate that the interfacial contact quality between Si and Fe2O3 is the dominant factor for determining ignition properties of thermites. Finally, the reaction onset temperature of the Si/Fe2O3 core/shell nanoparticles is comparable to the commonly used Al-based nanothermites, suggesting that Si is an attractive fuel for thermites.
2:15 PM - PM02.05.03
Tuning the Ignition Threshold of Ball-Milled Al:Zr Nanocomposite Powders Independent of Powder Size
Elliot Wainwright 1 , Mingyu Yang 1 , Shashank Vummidi Lakshman 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractAl/Zr reactive nanocomposite powders have been fabricated via arrested reactive milling (ARM) with ignition thresholds and combustion properties that can tuned independently by varying reactant spacing and particle size. Here we focus on ignition thresholds and show that the same low ignition temperature is measured using hot-filament methods for a broad range of distinct particle sizes: 0-10, 10-32, 32-53, 53-75, and >75 micron. We explain the nearly identical temperatures using data from SEM images and DSC scans. Large, stitched SEM images of hundreds of particles in each size range, characterized via MATLAB codes, show a consistent distribution in the spacing of the Al and Zr reactants. The DSC scans display a consistent set of exothermic peaks whose magnitude and temperature do not vary as a function of particle size. Together these data sets explain the uniform ignition temperatures observed over a broad range of Al/Zr particle sizes.
2:30 PM - PM02.05.04
Laser Ignition on Aluminum-Polymer Nanoenergetic Systems Using Plasmonic Gratings
Naadaa Zakiyyan 1 , Biyan Chen 1 , Matthew Riehn 2 , Aaron Wood 1 , Sangho Bok 1 , Rajagopalan Thiruvengadathan 1 , Cherian Mathai 1 , Syed Barizuddin 1 , Keshab Gangopadhyay 1 , Matthew Maschmann 2 , Shubhra Gangopadhyay 1
1 Department of Electrical and Computer Engineering, University of Missouri, Columbia, Missouri, United States, 2 Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, Missouri, United States
Show AbstractIn situ laser-induced ignition of nanoenergetic systems consisting of aluminum nanoparticles (Al NPs) embedded in polymer oxidizers were examined using optical microscopy and plasmonic gratings. The polymers of interest include Teflon, THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride) and nitrocellulose (NC), due to diverse physical and reactivity characteristics as well as processing feasibility. Two different sizes for Al NPs (80 nm and 120 nm in diameter) were investigated. Energetic thin films were cast on plasmonic gratings to enhance both the photothermal coupling and the spatial resolution of the optical microscope. The spatial resolution was sufficient to facilitate Al NP counting, while a high-speed camera and two-color pyrometry were used to quantify reaction mechanism and reaction temperature respectively. Electromagnetic simulations showed Al NP absorption peaks at wavelengths of 810 nm, 546 nm, and 310 nm representing a dielectric loss, dipolar, and quadrupolar plasmonic peaks for 120 nm Al NP in THV, respectively. The dielectric loss peak is independent of Al size because it is a material property. However, increasing the diameter of Al NP red-shifts and broadens the plasmonic peaks. The plasmonic peaks shift to longer wavelengths with the increasing refractive index of the polymer oxidizers from Teflon, THV, to NC. Based on the theoretical prediction by simulation, different laser wavelengths were selected to enhance the photothermal heating by maximizing coupling efficiency. For example, a 446 nm pulsed laser was chosen to couple the dipolar plasmonic mode of 80 nm Al NPs, while a 632 nm pulsed laser was used to couple 120 nm Al NPs.
Two different optical microscope setups were utilized for these studies. An epifluorescence microscope enabled laser illumination from the top side of the grating without the limitation of the transparency of the grating. An inverted microscope enabled laser illumination from the bottom side of a transparent grating and high-resolution in situ imaging under 100x objective. These setups open the capability of in situ imaging and analysis of single nanoparticle combustion using conventional optical microscopes. These in situ techniques provide a direct visualization of the phase change of polymer and measurement of local temperature for a better understanding of the combustion mechanism. Nano-flame combustion from small Al NP agglomerates and linear reaction propagation were observed for both 80 nm and 120 nm Al NPs. Based on flame temperature obtained from two-color pyrometry, the radiative energy release from combustion was estimated using modified Stefan–Boltzmann law, which in turn enabled determination of the number of reacted Al NPs. An optical scattering measurement technique was developed using polarized light microscopy to identify particle variation before and after the reaction and may be used to identify reaction sites and the number of particles reacted.
PM02.06: Additive Manufacturing of Energetic Materials I
Session Chairs
Tuesday PM, November 28, 2017
Sheraton, 3rd Floor, Hampton
3:15 PM - *PM02.06.01
Additive Manufacturing of Energetic Nanocomposites via Slurry Jetting Process
Keerti Kappagantula 1
1 , Ohio University, Athens, Ohio, United States
Show AbstractThis study presents a unique approach to additively manufacturing reactive nanocomposite energetic materials via slurry jetting process. Nanocomposite energetics are typically made up of a nanoscale fuel and a nano- to micron scale oxidizer. Such reactive materials have gained increased attention over the last two decades. It is very attractive to “print” these energetic nanocomposites into desired profiles. This can be achieved by building the desired profiles from a bottom up approach using additive manufacturing techniques. Such a manufacturing process development can prompt a rapid design – prototype manufacture – test – property improvement cycle for making nanocomposite energetic material parts desirable for ordnance, industrial and research applications. Such techniques are cost effective, facilitate precision placement of fuel/oxidizer particles for optimal combustion performance, and reduce material wastage.
In this study, slurry jetting process is used to manufacture nanocomposite energetic material parts of desired geometry. Energetic materials with surface chemistry similar to those of actual reactive nanocomposites are manufactured using nanoscale aluminum oxide particles as mock (inert) fuel material, and micron scale copper oxide particles as oxidizer. The printing process is similar to binder-jetting method, except the binder material is replaced with a printing liquid in the form of a slurry. The mock nanoscale fuel particles are housed in the printing liquid which is then deposited over an oxidizer powder bed. In addition to the mock fuel particles, the printing liquid also comprises of a solvent, a binding agent, and surfactants. Each layer of the desired component is printed by depositing the printing liquid in the desired geometry over the oxidizer bed, after which a new layer of oxidizer is introduced into the build chamber using a roller. Assembly of subsequent layers with desired geometry leads to the construction of the 3D printed reactive material part with the desired profile.
Printing liquid rheology, material resolution, compression strength of the printed reactive material part, manufacturing defects, microstructure of the printed components, and fuel/oxidizer distribution at the nano- to micron scale is explored in the present study as a function of nanoscale particle loading in the printing liquid. The present study demonstrates the viability of existing solid free form manufacturing techniques to as viable approaches to 3D print nanocomposite reactive material parts. The slurry jetting method used in the present study is a unique way to additively manufacture nanocomposite energetic material parts with desirable mechanical strength and is suitable for manufacturing propellants, solders, structural energetics, and pyrotechnics among other applications.
3:45 PM - PM02.06.02
Rheological Properties of Al-Zr Composite Powders Mixed in Hydroxyl-terminated Polybutadiene (HTPB)
Michael Tershakovec 1 , Elliot Wainwright 1 , Shashank Vummidi Lakshman 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States
Show AbstractAl-Zr based reactive composites are being developed for bio-agent defeat applications which require mixing with a binder, such as hydroxyl-terminated polybutadiene (HTPB). Optimization of the powder loading is desired to maximize energy density within the formulations. The viscosity of these highly concentrated, polymer-fuel suspensions needs to be low enough to easily injection mold or cast these formulations into usable forms. Factors such as powder morphology, relative density, powder size distribution, powder loading and the native mechanical properties of the polymer govern the viscosity of the fuel-polymer suspensions. In this work, we investigate the effect of fuel particle size distribution, powder loading percentages, and mixing temperature on the viscosity of HTPB loaded with powders to help understand and further develop these explosive formulations.
4:00 PM - PM02.06.03
3D Printing of Thermite Mixtures Using Static Mixing
Michael Grapes 1 , Matthew Durban 1 , Kyle Sullivan 1 , Alex Gash 1
1 Materials Science Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractWater-based solids-loaded inks are a general solution for 3D printing of functional materials, including reactive materials. While pre-mixed reactive materials inks are possible, it is desirable from a safety standpoint to formulate single-component inks which each contain only one reactant. These inks are essentially inert while separate and only achieve reactive properties when mixed, minimizing the quantity of reactive material present at any one time. We have been exploring various approaches to on-the-fly mixing of such single-component inks for 3D-printed reactive materials. In this talk, I will focus on Al/CuO thermites printed from single-component inks with on-the-fly “static” mixing. Commonly employed for two-part epoxies or dental materials, static mixers work by repeatedly “folding” two fluids together until they are intimately mixed. This is a useful alternative to dynamic mixing using a rotating paddle because it minimizes the energy input into the materials and thus the risk of premature reaction. The mixing quality is also less sensitive to variations in the printing speed. Our initial work has focused on demonstrating feasibility and identifying how much mixing, as characterized by the number of mixing elements, is required to achieve maximum thermite reactivity. After establishing the critical mixing conditions, we have explored some basic 3D-printed structures and begun to assess the impact of architecture on overall reactivity.
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-733101
4:15 PM - PM02.06.04
On the Fly Mixing and 3D Printing of Al/CuO Thermite
A. Golobic 1 2 , Matthew Durban 1 , Eric Duoss 1 , Alex Gash 1 , Kyle Sullivan 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States, 2 , University of California, Davis, Davis, California, United States
Show AbstractThe ability to spatially control the behavior of reactive materials within a part is now a reality with advances in 3D printing. This vastly opens up the design space for rapidly deflagrating materials, such as pyrotechnics or thermites, to yield a precise property or dynamic performance. In order achieve this goal, a mixing print head was used to mix an aluminum and a copper oxide ink on the fly. The mixing and printing parameters were first investigated for a stoichiometric mix of fuel and oxidizer to determine at what point the material can be assumed well-mixed. The equivalence ratio was then changed, and the critical mixing parameters established. The reactivity was characterized by printing a strip of material, then initiating the thermite and measuring the propagation velocity with a high-speed camera. Once the velocity reached a plateau, we considered the system well mixed. 3D printing was then used to make parts where the local stoichiometry, which corresponds to performance, is spatially varied. Collective effects of having incorporated features with differing reactivates were investigated.
4:30 PM - PM02.06.05
Additive Manufacturing of HTPB Based Energetics
Lori Groven 1 , Sharla Glover 2 , Derek Neubert 1
1 Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota, United States, 2 Mechanical Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota, United States
Show AbstractPrinting of HTPB based energetic materials has recently been of significant interest as a method to manufacture and study structured explosives and composite propellant formulations. While HTPB has a relatively low viscosity (6900 cP) in its neat form the addition of particulate significantly alters the rheological characteristics and typical energetic formulations have viscosities on the order of 5-20 McP.
A specific energetic material of interest is composite propellant (HTPB/AP/additives) used extensively in commercial and military applications. Composite propellant is currently cast into grains, which can be time consuming and costly. Transition to a fully printable formulation would allow for ease of manufacture on large and small scale. Such highly viscous materials have limited flow properties and present challenges when coupled with current printing technologies. To allow a formulation to be printable minimal modifications must be made to keep to the current standard burning rates and properties while allowing flow. The addition of solvents and other additives can be used to promote improved flow properties. These additions can create issues with the printing quality, strength of the material, hardness of the material, and burning rates. Optimization of formulations must be done to reach the correct amount of flow property modifiers. If these additives surpass a critical amount, issues with structural stability begin to prevent free standing structures from being printed.In this research, the development of a printable HTPB/AP propellant has been explored along with required methods for printing highly solids loaded materials. In this study, optimization of the formulation to reduce slumping and allow for proper structural integrity, along with keeping the material at th 85 wt% was a primary goal. Printing of structured rate sticks to test burning and structural properties of the resulting formulations was also conducted. It was found that depending on mixing technique rheology modifiers are not necessary and very high solid loaded formulations could be sucessfully printed with current off the shelf platforms.
PM02.07: Poster Session
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - PM02.07.01
Strained Glassy Organic Energetics
Rajen Patel 1 , Victor Stepanov 1
1 , U.S. Army, Picatinny Arsenal, New Jersey, United States
Show AbstractReactive materials are frequently used in combination with organic energetics to achieve ‘combined effects’. Often, research is focused on the inorganics in these formulations, usually so they can achieve more rapid and complete reactions. These ends can also be achieved by improving the organic portion of these mixtures. Borrowing from strategies used to enhance reaction rates in inorganic materials, ARDEC researchers are now working on highly strained organic energetics, the most strained being those in the amorphous state. Amorphous energetics offer tremendous advantages over their coarse crystalline counterparts, such as optical transparency, inherent strain energy, and processability via mechanical manipulation above the glass transition temperature. These materials can be produced scalably, and represent a fundamental improvement to the materials science of energetics. The basic properties of amorphous energetics will be discussed from bond length to mechanical properties. Future research directions, especially methods of incorporating inorganic reactive materials, will also be discussed.
8:00 PM - PM02.07.02
Investigation of Bimetal Thermite Powders on Their Reactivity and Aging Behaviors
Hongqi Nie 1 , Sreekumar Pisharath 1 , Huey Hoon Hng 1
1 , Energetics Research Institute, Nanyang Technological University, Singapore Singapore
Show AbstractNano-thermites comprising of a metal fuel (aluminum) and a metal oxidizer (CuO, Fe2O3 and MoO3, etc) in nano-scale are widely used as energetic additives in explosives and propellants. Higher reactivity for nanothermites is attributed to the superiority of kinetic control mechanism over diffusion control in determining the reaction rate between two constituents.
However, the practical applications of nanothermites are limited by the challenges of incomplete reaction owing to sintering and propensity to degradation by aging. Research works on Al-Ni reactions have experimentally indicated that, intermediate reaction products in metastable phase are formed well below the temperature at which the coalescence of nano-Al particles is most likely to occur. This could mitigate the effect of sintering on the performance of nanothermites. Furthermore, it has been reported that bimetal powders undergo oxidation at a slower rate as compared to n-Al, indicative of a lesser tendency to be aged for bimetal thermite powder. These aspects have not been investigated thoroughly in the context of nanothermites.
In this work, micron-sized nickel is mixed with Al/Fe2O3 nanothermite to fabricate bimetal thermite powder. The composition of nickel to the resulting bimetal thermites is varied from 5 to 20 weight %. The prepared materials are characterized by electron microscopy, X-ray diffraction and thermal analysis. Reaction completeness is assessed by comparing the experimental heat of combustion with the theoretical value. Aging studies are carried out by micro-calorimetry measurements using thermal activity monitor (TAM) at elevated temperatures under a controlled humid environment for both reference nanothermites and bimetal thermite powders. The effect of aging on the heat of combustion characteristics is investigated.
8:00 PM - PM02.07.03
Study of C/Doped δ-Bi2O3 Redox Reactions by In Operando Synchrotron X-Ray Diffraction
Xizheng Wang 1 , Daniel Taylor 1 , Michael Zachariah 1
1 , University of Maryland, College Park, Maryland, United States
Show AbstractWe employ in-situ X-ray diffraction to explore the reaction of carbon with metal oxides. In this paper, yttrium or tungsten doped δ-Bi2O3 were synthesized as oxygen carriers reacted with carbon black to study the performance of the oxygen carrier. The trajectory of the reaction of carbon/doped Bi2O3 was measured by in-operando synchrotron X-ray diffraction, from which the reaction kinetics was deduced. Heating rates were varied to determine the apparent activation energy for the carbon/doped Bi2O3 reaction. Results show that lower metal-oxygen bond energy and higher oxygen vacancy concentration of doped Bi2O3 led to lower onset temperature, faster reaction rate and smaller activation energy for carbon oxidation. These results provide important insights into manipulating oxygen carrier’s atomic properties for energetic applications.
8:00 PM - PM02.07.04
Polymer-Bound Reactive Materials Prepared by Additive Manufacturing
Jorge Castellanos 1 , Demitrios Stamatis 1 , Samuel Emery 1 , Sean Maharrey 1 , David Zamor 1 , Meagan Gay 1 , George McDaniel 1 , Austin Riggins 1 , Daniel Minehan 1
1 , RDT&E Department Naval Surface Warfare Center – Indian Head Explosive Ordnance Disposal Technology Division, Indian Head, Maryland, United States
Show AbstractCurrent scalable technologies (casting, pressing, ram and screw extrusion) for processing of energetic materials such as explosives, pyrotechnics, or propellants do not offer the flexibility to dispense material into unique, complex geometries that could impart a desired effect. The work herein seeks to exploit additive manufacturing to improve the combustion performance of test charges customarily filled with physical mixtures of reactive powders by printing paste forms into discrete annular arrangements. Charges were printed in with fuels of fine and coarse particle size as one gradient arrangement or fuel and oxidizer layers as a second arrangement. Anticipated enhanced effects obtained from closed-chamber detonation experiments include improved combustion efficiency, higher thermal output, and improved brisance, mainly quantified by dynamic and quasi-static pressure measurements. Potential applications include enhanced blast or underwater formulations.
8:00 PM - PM02.07.05
High Surface Area Porous Silicon Nanoparticles for Energetic Applications
Sarah Adams 1 2 , Nicholas Piekiel 1 , Matthew Ervin 1 , Christopher Morris 1
1 , US Army Research Lab, Adelphi, Maryland, United States, 2 , University of Maryland, College Park, College Park, Maryland, United States
Show AbstractCombustion of porous silicon has previously been explored both for particle formulations and for on-chip films. The latter has demonstrated excellent performance as indicated by flame speeds in excess of 3km/s, largely thanks to high surface area porous films (>800 m2g-1). The high flame speed and high energy density of porous silicon make it an interesting energetic material for a wide variety of applications, however its use is severely limited by the “on-chip” nature of this material. Flame speed measurements for porous silicon particle energetic formulations have not been explored as thoroughly, and the performance results are mixed. The lack of investigation is partly due to a lack of commercial availability of porous particles, and performance could be limited by particles with lower surface area than that of on-chip films. In this study, we fabricate high surface area porous silicon particles from on-chip porous silicon films. High surface area particulate porous silicon could expand the application to propellant additives or other traditional energetic applications, and potentially offer improved energetic performance. Particles with surface area upwards of 700 m2g-1 have been fabricated with open channel flame speeds approaching 1km/s. This study further considers the effect of porosity, pore size, particle size, and packing density on the energetic qualities of porous silicon nanoparticles. BET porosimetry, bomb calorimetry, TEM, DSC, and high speed imaging were used to analyze the physical and energetic qualities of the nanoparticles.
8:00 PM - PM02.07.06
Rapid Microwave-Assisted Synthesis of Zirconium Aluminide Alloys from Zr and Zr Hydride
Aryane Tofanello 1 , Waldemir Carvalho 1 , Sydney Santos 1 , Flavio De Souza 1 , Jean-Louis Bobet 2
1 , UFABC, Santo Andre Brazil, 2 , Université de Bordeaux , Bordeaux France
Show AbstractThe powder metallurgy industry has a high demand for new and improved sintering processes with finer microstructures for enhanced mechanical and physical properties. The microwave (MW) sintering process has several advantages over conventional sintering processes in many different fields, particularly ceramics. Herein, we describe a novel strategy for the direct syntheses of ZrAl alloys using the rapid microwave-assisted technique. A comparison between Zr and ZrH2 as starting precursors was performed and the microstructure, composition, density and microhardness of the obtained ZrAl alloys were investigated. The rapid microwave-assisted synthesis succeeded in producing the ZrAl alloys; however, this strategy enables access only to the Al-rich phase part of Zr-Al binary phase diagram. The method succeeded to synthesized ZrAl alloys resulting in ZrAl3 as the major product. Depending on the application and the desired impurities and properties, the Zr or ZrH2 could be more suitable. The ZrH2 samples showed a lower percentage of leftover Al and Zr, smaller particle size and higher initial microhardness. On the other hand, the Zr samples showed only ZrAl3 at the beginning and the possibility of increasing the ZrAl2 content with the MW time exposure. Furthermore, the ZrAl2 raise also increase the microhardness of the material (despite the grain growth of the sample) which can be more suitable for some applications. Finally, it is possible to control the final material properties according to the desired application by altering the Zr precursor and the MW exposure time. This work was supported by CNPq grant 400381/2014-1.
8:00 PM - PM02.07.07
Numerical Calculations and Energy Transduction Measurements in Electrically Exploded Aluminum-Boron Laminates
Christopher Morris 1 , David Lunking 1 , David Adams 2
1 , US Army Research Laboratory, Adelphi, Maryland, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe have shown evidence in the past of reactive mixing between nickel and aluminum over very fast time scales, and here we report on the aluminum/boron system. In the past, electrically exploded nickel/aluminum resulted in heating rates of 1011–1012 K/s, with the kinetic energy of an ejected parylene “flyer” layer successfully predicted by numerically modeling the partition of electrical input energy into sample heating, kinetic energy of the accelerating metal plasma beneath the flyer layer, and kinetic energy of the flyer layer itself. Model predictions matched experimental measurements only after including an additional energy term from the exothermic mixing of Ni and Al in the gas phase. These results were significant, because thermal diffusion processes normally limit Ni/Al reactions to much slower energy release rates. Here, we report on similar experiments and model predictions for aluminum-boron laminates, selected due to the higher energy density of the idealized aluminum-boron reaction. Boron is electrically resistive, so we designed many of the laminates to allow rapid heating through conduction from the rapidly-heated aluminum layers. However, there was no significant source of additional energy in any of the measured flyer kinetic energies, suggesting that exothermic mixing from aluminum and boron is either a very small fraction of the aluminum-boron reaction energy, or that exothermic mixing proceeds at much slower timescales, or a combination of both. This study therefore provides an interesting contribution to the body of literature on rapid reaction physics for reactive materials.
8:00 PM - PM02.07.08
Identification of Defect Density and Processing Induced Structural Variations in Molecular Organics Using Nanomechanical Testing
A. Burch 1 , A. Higginbotham Duque 2 , John Yeager 2 , David Bahr 1
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractMany reactive materials are used in crystalline solid forms which are subjected to a variety of processing methods, particularly powder processing. With the recent increase in advanced manufacturing techniques focusing on improved microstructural control, the local shear stresses during processing will likely increase over traditional plastic bonded systems. This current study uses nanoindentation of both energetic and simulant materials (materials with similar structures but no reactivity) in their as-processed state using conventional powder processing to demonstrate the local variations in mechanical properties. Sub-mm powders (on the order of 0.2 mm) of a variety of energetic materials were mounted and subsequently tested using indentation with spherical, obtuse, and acute indenter tip geometries at both low (1 mN) and high (100’s of mN) loads to examine the elastic-plastic transition; the hardness and modulus, and the propensity for fracture. In general, powders formed via precipitation or recrystallization exhibit yielding phenomena similar to those of mechanically fractured bulk (cm-scale) crystals, suggesting most powder forms will contain a significant existing dislocation density. Identification of relative fracture behavior using an unloading slope analysis of indentation load-depth curves showed that RDX and HMX exhibit a higher propensity for fracture than several simulant materials. Finally, statistical analysis of indentations of multiple crystal orientations was used to examine the fracture and yield behavior after accelerated aging at moderate temperatures, the rate dependency of hardness (albeit at relatively low loading rates) and to identify conditions which may cause transitions from plastic flow to fracture during future manufacturing processes.
8:00 PM - PM02.07.09
Characterization of Al/Ni Intermetallic Formed by Planetary Ball Milling at Low Temperature
Mingu Han 1 , Keundeuk Lee 1 , Sang-Hyun Jung 1 , SoJung Lee 1
1 , Agency for Defense Development, Daejeon Korea (the Republic of)
Show AbstractFor fundamental understanding of morphological and thermal characteristics for Al/Ni intermetallic materials prepared at low temperature, we synthesized intermetallics composed of 0.315 weight fraction of aluminum (obtained from Changsung) and the 0.685 weight fraction of nickel (obtained from Vale) by a planetary ball milling (PBM-150, Nanointech) at -50°C. The development of micro-structure phase between Al/Ni metals and compressive properties for compacts formed by the hydraulic press of prepared intermetallic powders under different pressures (2.3, 3.5, 5.3, and 7.0 kbar) were investigated depending on the milling time (15, 40, 60 min) using a differential scanning calorimetry (DSC), a scanning electron microscope (SEM), an universal testing machine (UTM). Moreover, the combustion behaviors of Al/Ni samples including the heat of combustion, the intensity of the reaction, and conformational/elemental change of compacts were compared with that of sample prepared at room temperature.
8:00 PM - PM02.07.10
Thermal Sensitivity in Al/Ni Reactive Powder System
Jooseung Chae 1 , Keundeuk Lee 1 , Sang-Hyun Jung 1 , Mingu Han 1 , Kibong Lee 1
1 , Agency for Defense Development, Daejeon Korea (the Republic of)
Show AbstractThe reactivity in Al/Ni reactive powder System due to thermal stimulus was investigated. Reactive systems with different microstructure formed by using three kinds of mixing processes were examined. The tubular mixer showed no effect in milling Al/Ni powder. In the attrition mill the shape of powder was distorted and grain size largely decreased from raw material. The planetary ball mill was useful to manufacture completely deformed powder with nano-lamella structure. In terms of interface state, these 3 types of powders are also clearly different according to observation of transmission electron microscopy. To compare the reaction initiation
temperature of these powders, differential scanning calorimetry analysis was performed. As a result, the reaction initiation temperature varied more than 350 oC according to the changes in microstructure. In order to compare reaction rate, thermal explosion phenomena of the 3 types of powder were also observed by high speed camera at a condition of 10,000 fps (frame per seconds). And it represents that the reaction rate also varies greatly depending on the microstructure of the powder. These results represent that reaction characteristics of reactive powder can be tailored by controlling the microstructure of reactive powder.
Symposium Organizers
Nicholas Piekiel, U.S. Army Research Laboratory
Steven Son, Purdue University
Karsten Woll, Karlsruhe Institute of Technology (KIT)
Xiaolin Zheng, Stanford University
Symposium Support
Lawrence Livermore National Laboratory
PM02.08: Additive Manufacturing of Energetic Materials II
Session Chairs
Wednesday AM, November 29, 2017
Sheraton, 3rd Floor, Hampton
9:00 AM - *PM02.08.01
Advances in Additive Manufacturing of Highly Viscous Energetic Materials
Lori Groven 1
1 Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota, United States
Show AbstractOver the past decade additive manufacturing has been considered a unique opportunity to develop materials in configurations that could not be considered previously. However, such techniques coupled to energetic materials have only recently been a major focus. Process methodology (formulations development/mixing), rheological characterization, and platform development all remain significant issues. At SDSMT we have made significant strides toward AM of a variety of highly viscous energetic materials and developed inks for composite propellant type materials, neat explosives, biological agent defeat formulations, as well as pyrotechnic materials (delay compositions and initiators). In this talk efforts in each of the areas will be discussed and the advances and limitations we have observed will be presented. For example, our group recently demonstrated that up to 85 wt% solids loading HTPB based materials could be printed using off the shelf AM techniques without the need for any processing aids (solvents) if the particle size distribution was optimized and the appropriate mixing technique was used. Free standing and filled structures have been demonstrated. Viscosity of such systems is on the order of 10-15 McP. Such techniques have been extended to explosive materials and up to 95 wt% solids loaded formulations have been printed in various geometries sucessfully.
9:30 AM - PM02.08.02
Ink Formulation and Direct Ink Writing of Thermites
Matthew Durban 1 , A. Golobic 1 , Eric Duoss 1 , Alex Gash 1 , Kyle Sullivan 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show Abstract3D printing is a rapidly emerging technology involving the layer-by-layer deposition of material to produce practical objects. This technique has great potential for reactive materials, in that dynamic behavior may be controlled through the strategic placement of material into features within an engineered part. Direct ink writing (DIW) is an extrusion-based method of 3D printing, involving the room temperature extrusion of custom inks through a micronozzle. Since heating is not required, DIW is suitable for printing reactive materials such as pyrotechnics or thermites. Here we investigate the formulation of both aluminum and copper oxide based inks for the direct printing of thermite materials. Solids loading, surfactant concentration, and matrix solvent (aqueous and non-aqueous) are all critical with regard to establishing an ink capable of shear thinning, but also rapidly setting upon extrusion. Without the latter behavior, the ink would sag upon printing and will not yield quality parts. The formulation and rheological properties of DIW inks are reported. We demonstrate the ability of each material to be extruded for 3D printing and discuss several parameters important to the process. Additionally, the components are mixed with a custom mixing head for the direct printing of a thermite composite.
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-717679.
9:45 AM - PM02.08.03
Additive Manufacturing of Composite Solid Propellant with High Solids Loadings
Monique McClain 1 , Ibrahim Gunduz 1 , Steven Son 1
1 , Purdue University, West Lafayette, Indiana, United States
Show AbstractSolid propellant performance is strongly dependent on the manufacturing process. The traditional method of casting propellant limits the ability to locally vary geometry and reactivity throughout the grain and could lead to the creation of defects. Additive manufacturing (AM) has been effectively demonstrated as an alternative manufacturing process for complex hybrid propellant grains. However, methods such as jet printing, stereolithography, and fuse deposition modeling are limited by the materials that can be printed. Printable materials are less reactive than baseline fuels, such as hydroxyl-terminated polybutadiene (HTPB), and high solids loadings have not been achieved, rendering the printing of high performing solid propellants unobtainable. In this paper, a new AM method was used to print ammonium perchlorate (AP) composite propellant strands at 85% solids loading. The viscosities of AP propellant mixtures were characterized to quantify printing parameters and the integrity of the samples were investigated with a digital microscope. The printed AP propellant strands were burned at pressure to determine the burning rate and were compared to cast samples with the same formulation. It was demonstrated that AM could be used to manufacture solid propellants at a solids loading comparable to current industry standards.
10:30 AM - *PM02.08.04
Exploiting Polymer Decomposition for the Production of Reactive Filament with Tailorable Thermal and Mechanical Properties
Jena McCollum 1 , Jose Bencomo 1 , Scott Iacono 2
1 , University of Colorado at Colorado Springs, Colorado Springs, Colorado, United States, 2 , United States Air Force Academy, Colorado Springs, Colorado, United States
Show AbstractRecently, there has been significant interest in using established additive manufacturing techniques to produce reactive composites. However, polymer property effects on energetic performance is still not well understood in this context. In this work, we explore melt-processing techniques to produce energetic filaments. This technique requires the use of a thermoplastic to serve as a host matrix for energetic particulate. Polymer matrices of poly(vinylidene fluoride) and poly(methyl methacrylate) were blended multi-scale aluminum fuel and tested for energetic performance. Binder formulations were examined below the solubility limits of PVDF-PMMA blends such that there was no phase separation in the polymer matrix. Results show that energetic performance is heavily dependent on thermal stability and decomposition characteristics of the polymer matrix. Thermal analysis (DSC/TGA), burn velocities, reaction products (XRD) and mechanical performance were assessed as a function of composition and geometry.
11:00 AM - PM02.08.05
Additive Manufacturing of Extremely Viscous Multifunctional Energetics
Ibrahim Gunduz 1 , Steven Son 1
1 , Purdue University, West Lafayette, Indiana, United States
Show AbstractRecent advancements in additive manufacturing (AM) for rapid prototyping allow precise geometric control of printed materials. By depositing layers of a material in a specific pattern layer by layer, one can fabricate very complicated multifunctional structures that would be difficult, if not impossible, with traditional manufacturing methods. The high geometric freedom accompanied with high resolution is appealing in many ways for the production of solid propellants or other deposited energetic materials. AM can also allow the study of complicated geometries that could produce tailored properties. We present recent efforts and approaches for a range of materials with different viscosities. We summarize our initial results in modified syringe printing of high-solids loaded propellants and fused deposition of pyrotechnic materials as multifunctional energetics. We have also investigated the utility of piezoelectric inkjet printers as nanothermite ink deposition systems, focusing on evaluating the feasibility to achieve the seamless integration of energetic material into small-scale electronic devices. These experiments quantified the effectiveness to heat, provide thrust, or fragment a silicon wafer.
11:15 AM - PM02.08.06
Characterizing Reactive Nanocomposite Particles for 3D Printed Electronic Interconnects
Shane Arlington 1 , Shashank Vummidi Lakshman 1 , Sara Barron 2 , Jeffery DeLisio 2 , Greg Fritz 2 , Timothy Weihs 1
1 , Johns Hopkins University - Materials Science, Baltimore, Maryland, United States, 2 , Charles Stark Draper Laboratory, Cambridge, Maryland, United States
Show AbstractRecent developments in additive manufacturing have highlighted the importance of rapid prototyping to assess product design and viability. However, for products with integrated electronics, the ability to 3-D print devices incorporating commercial off-the-shelf (COTS) electronic components has been limited to printers utilizing nanosilver inks. Due to nanosilver's high surface diffusivity at moderate temperatures, it can sinter at low temperatures resulting in electric interconnects with low resistivity. A downside of the high surface diffusivity is that these silver interconnects have poor durability due to electromigration, even at moderate current densities. Our goal is to design a reaction-assisted ink by ball milling multiple elements into composite powders, which will ultimately be added to a polymer matrix for printing. An interim investigation to determine optimal compositions and reactant spacing revolves around physical vapor deposited (PVD) particles and films, which have a much higher degree of uniformity and process control. The contain pairs of elements, such as Zr-C, Ti-C, and V-C, that have high heats of reaction, embedded in a soft matrix of Al or a Cu-Ag alloy. Upon heating, the pair of elements will react, helping to melt the soft matrix and form a robust interconnect. To assess feasibility and to characterize various powder chemistries and microstructures, we deposit the composite powders within a channel and then heat them to moderate temperatures using low, moderate, or high heating rates accomplished by a DSC furnace, a high-power pulsed lamp, and a laser raster respectively. The DSC furnace allows investigation of the total heat released by the reactive particles, where both the high-power lamp and the laser raster mimic commercially available 3D printers. Both air and inert environments are considered. We then measure the post-reaction electrical properties and we characterize morphologies and crystal structures using SEM and XRD.
11:30 AM - *PM02.08.07
Tailoring Reaction and Mechanical Properties of Reactive Composite Structures Made by Additive Manufacturing
Robert Reeves 1 , Christopher Shuck 1 , Michael Grapes 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractAdditive manufacturing techniques present a new methodology for creating highly customizable materials and structures. Incorporation of nano-composite reactive particles into additively manufactured processes provides the opportunity to create structures for which the mechanical properties and reaction behavior are both tailorable. Using a powder bed binder-based manufacturing technique, composite particles created through arrested ball-milling of elemental reactants were printed to create macroscopic structures. These structures were then infilled with a second material to create a nearly full-density composite consisting of reactive inclusions in a metallic matrix. The resulting material microstructure is characterized through optical and electron microscopy, as well as computed tomography. The bulk reaction behavior of the composite material, in terms of total available chemical energy and kinetics, is discussed in comparison to the green reactive powders. Mechanical properties, like density, strength and manufacturability, are also discussed as functions of the material set selected and the resultant micro- and macro-structure.
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
LLNL-ABS-717738
PM02.09: Nanocomposite Reactions I
Session Chairs
Wednesday PM, November 29, 2017
Sheraton, 3rd Floor, Hampton
1:30 PM - PM02.09.01
Controlled Destruction of Electromechanical Systems Using Printed or Deposited Confined Nanothermites
Eric Westphal 1 , Trevor Fleck 1 , Allison Murray 1 , Jeffrey Rhoads 1 , Ibrahim Gunduz 1 , Steven Son 1
1 , Purdue University, West Lafayette, Indiana, United States
Show AbstractThe rapid reactions in nanothermite systems make them suitable for integrated applications within electromechanical systems, such as controlled destruction of sensitive components. Previous work has demonstrated the ability of unconfined nanothermites to provide controlled substrate destruction. Thrust and heat deposited by these nanothermite mixtures have also been measured. In this study, the confinement of nanothermites was explored to characterize their performance. Fracturing of silicon wafers served as the method by which substrate destruction (fracture) was assessed during these experiments. Aluminum - bismuth (III) oxide and aluminum - copper (II) oxide nanothermite formulations were prepared at several equivalence ratios to study how the response can be tailored through mixture preparation. Nanothermite confinement using 3D printed structures has also been explored. Results were compared to previous work.
1:45 PM - PM02.09.02
Analyzing Thermite Reactions by the Direct Observation of Reacting Particles
Kyle Sullivan 1 , Michael Grapes 1 , Robert Reeves 1 , John Densmore 1 , Kamel Fezzaa 2 , Anthony Van Buuren 1 , Trevor Willey 1
1 , Lawrence Livermore National Lab, Livermore, California, United States, 2 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractThe reaction of rapidly deflagrating thermites is a highly complex process, and few experimental techniques can probe these phenomena in situ due to the small length and time scales required. Here we combine an extended burn tube test with time-resolved x-ray imaging at the Advanced Photon Source to directly observe the evolution of reacting thermite particles. A small mass of thermite is initiated at the closed end of a clear acrylic tube, which confines the reaction so that reacting particles are projected down the tube. Examining the reacting particles at different distances along the tube, we can extract both qualitative and quantitative data on thermite reaction mechanisms. We have performed this experiment on a range of thermite systems, yielding large, information-rich image sets that present a challenge for conventional analysis. Qualitatively, in all cases we observe evidence of particle coalescence and condensed-phase interfacial reactions. For quantitative analysis, we have explored a number of approaches to data reduction using metrics like particle count, particle size distribution, and x-ray absorptivity. We will present the latest results of these efforts, which are improving our understanding of the progression from reactants to products in these systems. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
2:00 PM - PM02.09.03
Characterization of Reactive Material Critical Mixing Time by Extended Burn Tube Tests
Maxwell Murialdo 1 , Michael Grapes 1 , Kyle Sullivan 1
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractRecently devised extended burn tube tests have shown promise in characterizing the burn time of reactive materials. Here our goal was to quantify the critical mixing conditions for reactive material formulations. We consider particle size, formulation, container and mixer settings in our experimental test matrix. Some systems were found to reach a plateau in the burn time above a finite mixing time, which we define as a critical mixing timescale. Other systems did not exhibit this behavior and will be discussed. Additionally, we consider alternate designs of the extended burn tube, which utilize a larger diameter of tube and a more robust igniter system. The interpretation and analysis of the luminous signal as a “burn time” will be discussed and improvements will be suggested. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release #: LLNL-ABS-733157
2:15 PM - PM02.09.04
Microexplosions and Bubble Growth Dynamics in the Combustion of Al:Zr Nanocomposite Powders
Elliot Wainwright 1 , Shashank Vummidi Lakshman 1 , Andrew Leong 1 , Alex Kinsey 1 , John Gibbins 1 , Shane Arlington 1 , Tao Sun 2 , Kamel Fezzaa 2 , Todd Hufnagel 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States, 2 Advanced Photon Source, Sector 32, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractAl/Zr reactive nanocomposite powders show promise as fuel additives in bio-agent defeat applications, and potentially in explosives and propellants as well. The powders are synthesized via high energy planetary ball-milling, and they have independently tunable ignition and combustion properties through variations in reactant spacing and particle size. Once ignited on a hot-filament, the particles fall off and burn in both vapor and condensed phases at 2700-3500 K and microexplode. Using synchrotron x-rays at the Advanced Photon Source (APS, 32-ID-B), we viewed the interior of the combusting particles via phase contrast imaging. Through simultaneous external high-speed imaging and spectroscopy, we can observe and correlate internal bubbling with luminous intensity spikes and gas production. We will present images showing heterogeneous nucleation and rapid growth of gaseous bubbles within the molten particles, and we will identify a critical rate of bubble expansion that is needed for microexplosion of the powders. Calculations of Laplace pressures and evaporation rates indicate that the high bubble expansion rates cannot be enabled by boiling of Al alone, corroborating previous studies of pure-Zr microexplosion mechanisms which require the presence of nitrogen. The current in situ observations provide a deeper understanding of the combined processes of bubble nucleation, growth, and coalescence, and the very rapid microexplosion events. This understanding, in turn, will enable the design of more effective metal fuel powders that include elements with high vapor pressures and high melting point compounds, allowing for control of bubble nucleation and growth and microexplosion properties.
PM02.10: Reactive Laminate II
Session Chairs
Wednesday PM, November 29, 2017
Sheraton, 3rd Floor, Hampton
3:30 PM - *PM02.10.01
Structure Property Relationships in Reactive Nanolaminates
Jon-Paul Maria 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractIn 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, and intermediate eutectic liquid formation, 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. Zr-CuO laminates were the least stable, owing to the fast oxygen transport through the ZrO2 terminal oxide, while CuO-Al laminates were the most stable, owing to the excellent diffusion barrier properties associated with Al2O3. Calorimetry analysis is used to measure effective activation energies for each material combination in order to better understand the material property / energy release relationships. Through this analysis we propose a modified Kissinger method to interpret kinetic data.
In addition, we report the use of ultrafast methods to interrogate the material properties and short time scale response of metal/metaloxide multilayers. These include time domain thermoreflectance (TDTR) to measure bulk and interfacial thermal transport, and flyer plate shock spectroscopy to observe how mechanical shock participates in the initiation of exothermic reactions.
4:00 PM - PM02.10.02
Reactive Nano-Laminates Analyzed Using a Combined Approach of First-Principles Calculations and Experimental Nanocalorimetry
Joost Vlassak 1
1 , Harvard University, Cambridge, Massachusetts, United States
Show AbstractThe extraordinary sensitivity and extremely small thermal mass of micromachined nanocalorimetry sensors allow the study of reactions and phase transformations in coatings and thin films over a broad range of heating rates, from isothermal to 105 K/s. Here we employ nanocalorimetry to investigate the synthesis of ZrB2 and carbon-doped ZrB2 using Zr/B and Zr/B4C reactive nanolaminates. ZrB2 is an ultra-high temperature ceramic that is the material of choice for applications involving optoelectronic devices, low-temperature fuel cells, and structural materials for hypersonic flight. The formation of ZrB2 in these multilayers is shown to proceed in two distinct steps: an inter-mixing/amorphization step, followed by a crystallization step. The inter-mixing process has a very low activation energy and the ensuing amorphization facilitates fast transport of B atoms into the Zr lattice. The presence of carbon in the nanolaminates further reduces the activation energies of inter-mixing and crystallization.
First-principles calculations provide insight in the amorphization processes in the Zr/B nanolaminates and confirm the relatively low activation energies associated with the processes. The simulations elucidate the effects of B concentration and temperature on the diffusion kinetics and phase evolution of the Zr-B alloys. Both C or N, which have strong binding energies with Zr, facilitate the amorphization and enhance inter-mixing of the layers in the coating. Based on this finding we suggest that elements with strong binding energies with transition metals can greatly facilitate the synthesis of diboride-based metallic ceramics.
4:15 PM - PM02.10.03
A Joint Theoretical/Experimental Study to Predict Al/CuO Nanolaminates Thermal Ageing
Guillaume Lahiner 1 2 , Iman Abdallah 1 , James Zapata 1 , Mehdi Djafari Rouhani 1 2 , Alain Estève 1 2 , Carole Rossi 1 2
1 , LAAS-CNRS, Toulouse France, 2 , Université de Toulouse, Toulouse France
Show AbstractEnergetic materials are the only attractive sources of “dormant” energy, enjoying long shelf life (decades), that can deliver quick on-demand bursts of energy in the form of heat and/or pressure. Among the large variety of energetic materials, reactive nanocomposites, based on exothermic thermite reactions, are attracting great attention, with the investigation of different types of reactive mixed nanopowders. A less common method is to sputter deposit alternating layers of Al fuel and oxide (mostly CuO) to form nanolaminate films. This category of reactive nanocomposites is very interesting for on-chip integration and have been applied in many applications such as in micro initiators, MEMS heat sources for welding or soldering or exploding foil initiators for several reasons. Although the integration of energetic materials with other microscale devices has been studied and demonstrated for more than a decade, the prediction of material ageing which is a key issue for a system supposed to stay in sleeping mode for decades, is inexistent. This work proposes a synergistic theoretical/experimental approach to unravel ageing mechanisms in Al/CuO nanolaminates as well as to enable the prediction of initiation and combustion properties after long time ageing periods at room temperature, or under higher temperature constraints ranging from 200 to 400 °C.
We perform systematic DSC measurements (Differential Scanning Calorimetry) run with different heating rates and apply an isoconversional thermokinetic method to determine values of the activation energy, as a function of the reaction progress, without assuming a priori any particular reaction mechanisms. The obtained kinetic parameters are then utilized to model materials evolution at various temperatures in isothermal conditions. First results predicted that for a storage at a temperature lower than 250°C, the Al+CuO reaction progresses very slowly on the time scale of months for both Al/CuO and CuO/Al foils. Based on these findings, we performed a set of physico-chemical and structural characterizations, implying TEM (Transmission Electron Microscopy) and XRD (X-ray Diffraction) techniques, on both systems annealed to various temperatures (200, 350, 500 and 700 °C). This allows understanding the fundamental mechanisms involved during thermal ageing such as atomic diffusion, crystallization, and formation of new species (alloys). We also characterized structures annealed at different temperatures. We demonstrate that both interfaces ageing proceed through specific and contrasted mechanisms both resulting in the formation of ternary CuAl2O4 alloys. Their respective resistance to ageing is also discussed and quantified.
This work gives perspectives for a phenomenological level of modelling, which will integrate the most pertinent identified mechanisms and created species to predict initiation and combustion of aged nanolaminates.
Symposium Organizers
Nicholas Piekiel, U.S. Army Research Laboratory
Steven Son, Purdue University
Karsten Woll, Karlsruhe Institute of Technology (KIT)
Xiaolin Zheng, Stanford University
Symposium Support
Lawrence Livermore National Laboratory
PM02.11: Novel Reactive Materials
Session Chairs
Thursday AM, November 30, 2017
Sheraton, 3rd Floor, Hampton
9:00 AM - *PM02.11.01
Spray Assembled Nanomaterials and Their Combustion Properties
H. Wang 1 , Rohit Jacob 1 , Phil Guerieri 1 , Miles Rehwoldt 1 , Michael Zachariah 1
1 , Univ of Maryland, College Park, Maryland, United States
Show AbstractOne 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. A range of architectures can be achieved, as we have demonstrated nanofibers, mesoparticle and films.
We find that the combustion properties of these material almost always results in more complete combustion, and fast burning speeds than the same components homogenously mixed. Combustion mechanisms are discussed.
9:30 AM - PM02.11.02
Creating Reactive Core-Shell Nanoclusters Using Superfluid Helium Droplet Synthesis
Kyle Overdeep 1 , Brian Little 1 , Claron Ridge 1 , Dylan Slizewski 1 , Christopher Crouse 1 , C. Michael Lindsay 1
1 , Air Force Research Laboratory, Eglin AFB, Florida, United States
Show AbstractSuperfluid Helium Droplet Assembly (SHeDA) is a method by which it is possible to create stable nanoclusters and soft-deposit them onto a substrate. With this technique, helium droplets pass through a vapor cloud of nearly any material heated in an effusion oven. The atoms that collide with the helium condense into clusters at the center of the droplet. It is our goal to use SHeDA to fabricate reactive core-shell nanoclusters by first passing the helium droplets through Al vapor to form a metallic core, followed by a vapor of perfluoropolyether (PFPE) that forms an external shell. This combination of materials is highly energetic due to the high oxygen and fluorine content in PFPE. The droplets maintain a temperature of 0.4 K which freezes out potential reactions between components and encourages the formation of a metastable un-mixed state. The PFPE exterior may also provide passivation against the atmospheric conditions post-fabrication. The stability of the resulting clusters are tested using Temperature Programmed Reactions (TPR) and viewed using Transmission Electron Microscopy (TEM). TPR is performed on nanoscale and microscale mixtures of vapor-deposited layers and physically mixed particles of the same compositions for comparison.
9:45 AM - PM02.11.03
Synthesis and Characterization of a 3D-Macroscale RGO/Al/Bi2O3 Nanoenergetic Organogel
Anqi Wang 1 , Sangho Bok 2 , Rajagopalan Thiruvengadathan 2 , Syed Barizuddin 2 , Cherian Mathai 2 , Matthew Maschmann 3 , Keshab Gangopadhyay 2 , Shubhra Gangopadhyay 2
1 Bioengineering, University of Missouri, Columbia, Columbia, Missouri, United States, 2 Electrical and Computer Engineering, University of Missouri, Columbia, Columbia, Missouri, United States, 3 Mechanical and Aerospace Engineering, University of Missouri, Columbia, Columbia, Missouri, United States
Show AbstractNanoenergetic materials have attracted a great deal of attention over the past two decades due to realization of tunable and tailorable, yet enhanced combustion performance. The fundamental challenges to employing nanoenergetic materials in practical applications include particle aggregation, stability and handling of nanoscale powders. Our study presents a novel method that overcomes many of these challenges. Specifically, we demonstrate a one-pot synthesis procedure to form a 3D macroscale energetic gel that is composed of aluminum nanoparticles (Al NPs), bismuth oxide (Bi2O3) NPs and functionalized graphene. Functionalized graphene enhances the chemical stability, mechanical properties, and also energetic performance of the organogel with reduced sensitivity to electrostatic discharge.
In this work, a novel chemical reduction method was employed to synthesize 3D macroscale (from mm to cm) RGO/Al/Bi2O3 nanoenergetic organogel. Depending on the relative amounts of the constituent nanoenergetic material, the density of the resulting organogel ranged from 20 to 200 mg/cm3. Individual dispersions of GO, Al NPs, and Bi2O3 NPs in propylene carbonate (PC) were first prepared and homogeneously mixed using an ultrasonic bath. A chemical reduction process was carried out using ethylenediamine (EDA) to reduce GO to RGO. Specifically, the π-π interaction between RGO sheets facilitated a formation of a 3D organogel with micrometer sized pores. Freeze drying preserved the structure and porosity of the gel.
The organogel was characterized using scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD) and differential scanning calorimeter (DSC). The homogeneity in the spatial distribution of Al and Bi2O3 NPs was confirmed by SEM imaging and EDS elemental mapping. Significantly, the commonly reported observation of phase separation of Al and Bi2O3 NPs in neat Al/Bi2O3 nanocomposite was overcome through organogel formation, and particles were confined within the graphene sheets. Further, agglomeration of either the fuel or the oxidizer NPs was absent. The SEM images confirmed the porosity of the formed structure created by RGO framework. The XRD results of the organogel confirmed the absence of any unwanted reaction of Al and Bi2O3 NPs with EDA, which was a selective reducer in PC that reduced GO to RGO without reducing Bi2O3 to Bi metal. The energy release from the exothermic reaction of the organogel determined from the DSC thermogram was 967 ± 17 J/g, which is 29% higher than the value of 749 ± 16 J/g obtained for a neat control sample of Al/Bi2O3. The enhanced energy release reaffirmed the significantly reduced phase separation between oxidizer and fuel as also confirmed from SEM imaging. Preservation of nanoscale properties of fuel and oxidizer NPs in a 3D organogel and enhanced energy release hold great promise towards safe handling of the material with myriad applications.
PM02.12: Novel Diagnostics
Session Chairs
Thursday PM, November 30, 2017
Sheraton, 3rd Floor, Hampton
10:30 AM - *PM02.12.01
In Situ Characterization of Nanoenergetics
Shubhra Gangopadhyay 1 , Biyan Chen 1 , Naadaa Zakiyyan 1 , Connor Wolenski 1 , Aaron Wood 1 , Syed Barizuddin 1 , Cherian Mathai 1 , Sangho Bok 1 , Rajagopalan Thiruvengadathan 1 , Matthew Maschmann 2 , Keshab Gangopadhyay 1
1 Electrical and Computer Engineering, University of Missouri, Columbia, Missouri, United States, 2 Mechanical and Aerospace Engineering, University of Missouri, Columbia, Missouri, United States
Show AbstractNanoenergetics continues to receive attention because of defense and civilian applications such as microinitiators, microthrusters, and medical therapeutic devices. In situ characterization of nanoenergetic systems is a key for understanding the reaction kinetics. The advances of in situ microscopy and spectroscopy enable time-resolved and quantitative measurements of nanoenergetic systems. Here, we employ plasmonic gratings in synergistic combination with optical microscopy and Raman spectroscopy besides performing in situ transmission electron microscopy(TEM) heating study. The grating enhances the efficiency of photothermal conversion by plasmonic coupling of laser to nanoenergetic materials and also improves optical measurement due to high signal-to-noise ratio. The aluminum nanoparticles(Al NPs) and few layered molybdenum trioxide(MoO3) or a fluoropolymer(THV:tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride) have been used to prepare nanoenergetic composite.
In situ optical microscopy employs an epifluorescence microscope with a high-speed camera. A 446nm pulsed laser excites a drop-casted film of Al NPs embedded in THV to study the reaction of individual Al NPs and clusters. The gratings enhance a spatial resolution of a microscope down to 200nm and lower the ignition energy resulting in a combustion of Al NPs with a low laser fluence(1.8×105J/m2). The temperature of nanoflames(400-600nm) from Al NPs is estimated to be 2300-4000K by two-color pyrometry.
In situ Raman spectroscopy uses the grating to study Al NPs on α-MoO3 flakes. Al NPs are photothermally heated via exposure to a laser(632nm with 1μm diameter) for local Al NP ignition. A significant jump in the Raman spectra baseline intensity is seen as the reaction occurs. The intensity reduction of MoO3 peaks and the peak observed at 418cm-1 is due to the formation of α-Al2O3 formed by high reaction temperature. Through tuning the spectral acquisition time, the time between acquisitions, and the number of accumulations, we have a better understanding of the reaction phenomenon.
In situ TEM heating examines the reaction of Al NPs and MoO3 flakes. A dispersion of Al NPs and MoO3 is deposited onto a TEM heating membrane. Samples are heated at a rate, 1 K/s. Al diffusion through the encapsulating alumina shell are observed at 600oC with rapid Al ejection occurring at approximately 650oC. Significant mobility of MoO3 is observed at temperatures as low as 400oC, increasing the intimacy between Al and MoO3. During reaction, the rapid formation of solid alumina sheets is observed. These sheets form in high aspect ratio and decorate the evacuated alumina shells of reacted NPs. The sheets may provide a barrier to prevent agglomeration of Al NPs during reaction, retaining the reactive surface area while providing a pathway for heated reaction gases. Thus, we demonstrate a novel characterization tool to probe the reaction pathways of individual or a cluster of Al NPs with oxidizer in situ.
11:00 AM - PM02.12.02
Probing the Oxidation Mechanisms of Tantalum Nanoparticles and Nanothermites at High Heating Rates
Jeffery DeLisio 1 , Xizheng Wang 1 , Tao Wu 1 , Garth Egan 1 , Rohit Jacob 1 , Michael Zachariah 1
1 , University of Maryland, College Park, Maryland, United States
Show AbstractReduced diffusion length scales and increased specific surface areas of nanosized metal fuels have recently demonstrated increased reaction rates for these systems, increasing their relavence in a wide variety of applications. In addition, nanopowders of a wide variety of metals are now commercially available. In this study, tantalum nanoparticles were chosen due to its high melting point (3017 oC) in comparison to aluminum (660 o C), the most commonly employed and extensively studied metal fuel. Previous studies on the oxidation of aluminum nanoparticles have shown the importance of oxide shell crystallization, but analyzing its effect at timescales relevent to combustion is difficult due to aluminum melting during oxide crystallization. Analogously, it has been observed that an amorphous to crystalline transition in Ta2O5 thin films begins at ~500 oC with crystallization occurring rapidly at higher temperatures, however unlike Al, the effect of the oxide shell crystallization on ignition of tantalum nanopowders can be probed without interference from melting.
Tantalum nanoparticles were studied using TGA/DSC, temperature jump ignition, and high heating rate TEM analysis to probe the role of oxide shell crystallization in the oxidation mechanism of tantalum nanoparticles and nanothermites. When oxidized by gas phase oxygen, the oxide shell of the tantalum nanoparticles rapidly crystallized creating cracks that may attribute to enhanced oxygen diffusion into the particle. In the case of tantalum based nanothermites, oxide shell crystallization was shown to induce reactive sintering with the metal oxide resulting in a narrow range of ignition temperatures independent of the metal oxide used. The oxidation mechanism was also modeled using the Deal-Grove model for silicon oxidation and theoretical burn times for tantalum based nanocomposites were calculated.
11:15 AM - PM02.12.03
Chemical Dynamics of Nano-Aluminum and Iodine Based Oxidizers
Brian Little 1 , Claron Ridge 1 , Kyle Overdeep 2
1 Energetic Materials Branch, University of Dayton Research Institute @ AFRL/RWME, Eglin AFB, Florida, United States, 2 Energetic Materials Branch, National Research Council @ AFRL/RWME, Eglin AFB, Florida, United States
Show AbstractAs observed in previous studies of nanoenergetic powder composites, micro/nano-structural features such as particle morphology and/or reactant spatial distance are expected to strongly influence properties that govern the combustion behavior of energetic materials (EM). In this study, highly reactive composites containing crystalline iodine (V) oxide or iodate salts with nano-sized aluminum (nAl) were blended by two different processing techniques and then collected as a powder for characterization. Physiochemical techniques such as thermal gravimetric analysis, calorimetry, X-ray diffraction, electron microscopy, high speed photography, pressure profile analysis, temperature programmed reactions, and spectroscopy were employed to characterize these EM with emphasis on correlating the chemical reactivity with inherent structural features and variations in stoichiometry. This work is a continuation of efforts to probe the chemical dynamics of nAl-iodine based composites.
11:30 AM - *PM02.12.04
Estimating the Relative Energy Content of Reactive Materials Using Nanosecond-Pulsed Laser Ablation
Jennifer Gottfried 1
1 , U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Show AbstractRecently, a laboratory-scale method for measuring the rapid energy release from milligram quantities of energetic material has been developed based on the high-temperature plasma chemistry induced by a focused, nanosecond laser pulse. The ensuing exothermic chemical reactions result in an increase in the laser-induced shock wave velocity compared to inert materials.1 The laser-induced air shock from energetic materials (LASEM) method provides a method estimating the detonation performance of novel organic-based energetic materials prior to scale-up and full detonation testing.2-4 Here, the extension of LASEM to non-organic energetic materials is discussed. The laser-induced shock velocities from reactive materials such as Al/PTFE,5 Al/CuO,6 Al/Zr alloys,7 and porous silicon composites8 have been measured; in many cases, the high sensitivity of the samples resulted in propagation of the reaction to the surrounding material, producing significantly higher shock velocities than conventional energetic materials. Methods for compensating for this effect will be discussed. Despite this limitation, the relative comparison of the shock velocities, emission spectra, and combustion behavior of each type of material provides some insight into the mechanisms for increasing the energy release of the material on a fast (µs) and/or slow (ms) timescale.
1 J. L. Gottfried, "Influence of exothermic chemical reactions on laser-induced shock waves," Phys. Chem. Chem. Phys. 16, 21452-21466 (2014).
2 J. L. Gottfried, "Laboratory-scale method for estimating explosive performance from laser-induced shock waves," Propellants Explos. Pyrotech. 40, 674–681 (2015).
3 J. L. Gottfried and E. J. Bukowski, "Laser-shocked energetic materials with metal additives: evaluation of chemistry and detonation performance," Appl. Opt. 56, B47-B57 (2017).
4 J. L. Gottfried, T. M. Klapötke, and T. G. Witkowski, "Estimated detonation velocities for TKX-50, MAD-X1, BDNAPM, BTNPM, TKX-55 and DAAF using the laser-induced air shock from energetic materials technique," Propellants Explos. Pyrotech. 42, 353-359 (2017).
5 T. R. Sippel, S. F. Son, and L. J. Groven, "Aluminum agglomeration reduction in a composite propellant using tailored Al/PTFE particles," Combust. Flame 161, 311-321 (2014).
6 H. Wang, G. Jian, G. C. Egan, and M. R. Zachariah, "Assembly and reactive properties of Al/CuO based nanothermite microparticles," Combust. Flame 161, 2203-2208 (2014).
7 K. R. Overdeep, K. J. T. Livi, D. J. Allen, N. G. Glumac, and T. P. Weihs, "Using magnesium to maximize heat generated by reactive Al/Zr nanolaminates," Combust. Flame 162, 2855-2864 (2015).
8 A. Abraham, N. W. Piekiel, C. J. Morris, and E. L. Dreizin, "Combustion of Energetic Porous Silicon Composites Containing Different Oxidizers," Propell. Explos. Pyrotech. 41, 179-188 (2016).
PM02.13: Nanocomposite Reactions II
Session Chairs
Thursday PM, November 30, 2017
Sheraton, 3rd Floor, Hampton
1:30 PM - *PM02.13.01
A Gibbs Formulation for Reactive Materials with Phase Change and Chemistry
D. Scott Stewart 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractA large class of applications that include energetic materials have pure, condensed phase constituents that come into contact, chemically react and simultaneously undergo phase change. Phase change in a given molecular material is often considered separately from chemical reaction. Continuum phase field models often use an indicator function to change the phase in different regions according to an evolutionary (Ginzburg-Landau) equation. But chemical kinetic descriptions of change (according to physical chemistry formulations) count species or component concentrations and derive kinetic evolution equations based on component mass transport. We argue the latter is fundamental and that all components, designated by both phase and chemical characteristics should be treated as distinct chemical species. We pose a self-consistent continuum, thermo-mechanical model based on specified Gibbs potentials for all relevant components that are present in a single material. Therefore a single stress tensor, and a single temperature is assumed for the material for all relevant component-species, for all equilibrium potentials, interaction energies and material properties. We discuss recent examples, drawn from modeling both propellants and explosives, where we have applied the Gibbs formulation to model the behavior of complex reactive materials.
2:00 PM - PM02.13.02
What Atomic Properties of Metal Oxide Control the Initiation Temperature with Fuels (Al, B, C, Ta)
Xizheng Wang 1 , Michael Zachariah 1
1 , University of Maryland, College Park, Maryland, United States
Show AbstractThe purpose of this talk is to consider and explore what atomic properties of metal oxide control the initiation of reaction between different fuels and metal oxide. In this study, two different systematic doped metal oxides: perovskites and δ-Bi2O3, were synthesized by aerosol spray pyrolysis. Within each system, the crystal structure and morphology were maintained. Four fuels (Al, B, Ta, C) with different physical properties were included in this study. The initiation temperature of the fuels and doped metal oxides was measured by fast heating (> 105 K/s) temperature-jump/time-of-flight mass spectrometry coupled with high-speed imaging. These results were then correlated with the average bond energy and overall metal-oxygen electronegativity difference of doped metal oxide. In general, within each systematic metal oxide, we found linear relationships between average bond energy and electronegativity of metal oxides with the initiation temperature for almost all four fuels although they have completely different physical properties. These results indicate that intrinsic atomic properties of metal oxide mainly control fuel-metal oxide initiation.
2:15 PM - PM02.13.03
Rapid Reactions in Fully Dense Reactive Nanocomposite Materials
Ian Monk 1 , Mirko Schoenitz 1 , Edward Dreizin 1
1 , New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractReactive nanocomposite materials prepared by arrested reactive milling (ARM) form micron-sized, fully
dense particles. For most thermite compositions, ARM-prepared particles are made up of a fuel matrix
with nano-sized oxidizer inclusions dispersed throughout. In recent experiments, multiple ARM-
prepared thermites with aluminum as a fuel and several oxides as oxidizers were ignited by an
electrostatic discharge (ESD) and by a CO2 laser beam. Different heating rates were achieved with
different ignition sources. In ESD, the heating rate was close to 109 K/s, whereas in the CO2 laser beam,
the particles were heated at ca. 106 K/s. It was observed that the heating rate directly affects the burn
rate of these materials. The burn times of the laser-ignited particles were much longer than those of
particles ignited by ESD. This work is aimed to understand the mechanisms of combustion in such
materials following their rapid heating. Fuels including Al, Mg, and Zr were milled with different
oxidizers including CuO, Bi2O3, Fe2O3, MoO3, WO3, and S to create the desired reactive composites.
Experiments were aimed to quantify the burn rates of all prepared materials ignited in both ESD and CO2
laser beam. In ESD ignition experiments, the powders were placed on the tip of a needle-like electrode,
to minimize the number of particles ignited in each experiment and thus to avoid collective, cloud
combustion effects when quantifying the particle burn rates. A model of combustion of rapidly heated
particles was considered accounting for heterogeneous reactions occurring in the metal-oxidizer
interfaces and characterized earlier for low-temperatures leading to the particle ignition. Here, the
reaction kinetics quantified for low temperatures for the aluminum-based thermites (i.e., Cabrera-Mott
reaction followed by the reaction limited by diffusion of components through the growing alumina layer
experiencing polymorphic phase changes) was applied to extrapolate the reaction rates in these
materials at much higher temperatures, typical of their combustion. Different heating rates were
considered. Reactive interfaces in the composite particles were described accounting for the
experimentally characterized dimensions of the oxidizer inclusions in the metal matrix. It was observed
that varying the heating rate changes the rate of high-temperature reaction dramatically. At sufficiently
high heating rates, similar to those achieved in ESD ignition experiments, the complete redox reaction
was predicted to occur in the composite particles in the time scales comparable to their experimentally
observed burn times.
PM02.14: Powder Combustion of Metals and Alloys II
Session Chairs
Thursday PM, November 30, 2017
Sheraton, 3rd Floor, Hampton
3:30 PM - *PM02.14.01
Comparison of Reactive Ni/Al Structures Produced by PVD, Ball-Milling and High Pressure Torsion
Claus Rebholz 1 , Ibrahim Gunduz 2 , Charalabos Doumanidis 3
1 Mechanical and Manufacturing Engineering Department, University of Cyprus, Nicosia Cyprus, 2 School of Mechanical Engineering, Purdue University, West Lafayatte, Indiana, United States, 3 Department of Mechanical Engineering, Khalifa University of Science, Technology and Research, Abu Dhabi United Arab Emirates
Show AbstractExothermic formation reactions in nickel/aluminium (Ni/Al) reactive structures have been studied extensively in recent years. The main deposition methods used to produce such structures are physical vapour deposition (PVD), which allows the precise control on the nanoscale for the individual Ni/Al layers, and ball-milling (BM). While in BM the same microstructural uniformity cannot be achieved, the capital costs are lower and higher throughputs are possible compared to PVD, which is a relatively expensive and time consuming method for large scale manufacturing. Moreover, BM particulates can be cold-pressed into pellets, sandwiched into ductile foils, or incorporated into self-heating/sintering powders for practical applications. In this work, we introduce another mechanical method to produce reactive materials – high pressure torsion (HPT) – and compare the microstructures and self-propagating reactions in Ni/Al lamellas to those produced by PVD magnetron sputtering and low-energy BM. Self-propagating reactions, observed using high-speed optical camera and infrared thermometry, show that although the reaction velocities in materials produced by BM and HPT are approximately one order of magnitude lower, the results are similar in terms of exothermic responses and phase formation sequence. Various geometries, similarities and possible applications are discussed.
4:00 PM - PM02.14.02
Unique Combustion Behavior Observed for Al-C-Zr Composite Powders
Shashank Vummidi Lakshman 1 , Cong You 1 , Elliot Wainwright 1 , Tao Sun 2 , Kamel Fezzaa 2 , Todd Hufnagel 1 , Timothy Weihs 1
1 , Johns Hopkins University, Baltimore, Maryland, United States, 2 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractMetals such as aluminum and zirconium have distinct combustion behavior. Aluminum, based on its size and combustion regime will either combust in the vapor phase forming AlO or through surface-limited oxidation, while zirconium burns in the condensed phase often exhibiting brilliant micro-explosions. Our previous work and the studies of others have documented the effect of nitrogen as the primary driver for the micro-explosion mechanism in Zr. In the present work, we discuss the effect of carbon on the combustion behavior of Al-Zr composite particles prepared by high energy ball milling. More specifically, we demonstrate that carbides or carbon itself can alter the combustion behavior of Al-Zr particles by influencing the nucleation of nitrogen bubbles in the condensed phase and through the formation of an extended carbon flame surrounding the burning particles. Upon ignition of the Al-C-Zr composite particles, they form a molten Al-C-Zr-O-N solution that burns readily in air above 3000K. Given carbon readily reacts with Zr to form ZrC (1.903 kJ/g formation energy), and given carbide has a very high melting temperature (3800K), we expect small ZrC particles to form in the molten solution. These carbide particles can then act as nucleation sites for the N-bubbles that form in the molten droplets. We confirm this hypothesis by performing phase contrast imaging using the high-energy synchrotron X-rays at the Advanced Photon Source beamline 32-ID-B. Dramatic increases in nucleation rates of nitrogen bubbles are observed, due to the addition of carbon. The presence of carbon in the system also generates extended carbon flames that measure several times the diameter of the particles. This phenomenon is distinctly observed in the 30Al20C50Zr (at%) composite particles. The burning carbon in these extended flames acts as heated zones where the nano-alumina soot (a product of vapor-phase aluminum combustion) coalesce to form molten alumina droplets. In the phase contrast imaging videos, we observe coalescence of small alumina droplets, which are then drawn towards each other to form larger and larger droplets via Ostwald ripening. These molten alumina droplets often trace their parent Al-C-Zr particles, thereby forming a trail in the extended flame. We present both high-speed color and X-ray phase contrast videos describing the unique combustion behavior for the Al-C-Zr system.
4:15 PM - PM02.14.03
Doping Boron for Improved Ignition and Combustion
Kerri-Lee Chintersingh 1 , Mirko Schoenitz 1 , Edward Dreizin 1
1 Department of Chemical, Biological and Pharmaceutical Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States
Show AbstractBoron has been extensively studied due to its high gravimetric and volumetric heating values, which makes it a great candidate as a fuel additive for propellants and explosives. However it has yet to reach its full potential because of its lengthy combustion times and ignition delays. This work focuses on increasing the rate of heterogeneous combustion reactions on the surface of burning boron particles. The approach is to introduce small amounts (less than 5 wt%) of metals as catalytic additives or dopants to boron. The metals considered include iron, nickel, and manganese, expected to readily oxidize heterogeneously at the temperatures at which boron burns, and, at the same time, expected to be readily reduced by boron. The materials are prepared using 95% pure commercial boron and higher purity, 99%, boron powders by wet chemistry, milling and other techniques. The prepared samples are characterized using scanning electron microscopy to observe surface morphology and particle size distribution. Flame temperatures and burn times are measured from optical emissions of single burning particles laser ignited in air, burning in the combustion products of a pre-mixed air- acetylene and a diffusion hydrogen- oxygen flames. Correlations of particle size and burn times indicate that the effect of dopants on combustion is stronger in air and hydrogen- oxygen environments. The combustion temperatures recorded are approximately 2800 K, with negligible difference when additives are included. However, the emission intensity produced by burning doped particles is reduced compared to that for as received boron. The effects of boron purity, dopant loading, dopant type, preparation technique and combustion environment will be discussed.