M. Riad Manaa Lawrence Livermore National Laboratory
Choong-Shik Yoo Washington State University
Evan J. Reed Stanford University
Michael S. Strano Massachusetts Institute of Technology
Y1: Synthesis, Formulation and Characterization
Monday PM, November 28, 2011
Room 309 (Hynes)
9:15 AM - **Y1.1
WITHDRAWN 11/16/11 New Energetic Materials.
Gregory Drake 1 , Sarah Bolden 1 , Jami Dailey 2 Show Abstract
1 Energetics Function, U.S. Army AMRDEC RDMR-WDP-E, Huntsville, Alabama, United States, 2 , ERC, Inc., Huntsville, Alabama, United States
Our recent efforts have centered on several classes of energetic materials in trying to decipher some of the relationships between molecular shapes and physical properties. Discussions will include both neutral and charged heterocyclic and aliphatic based energetic materials.
10:00 AM - Y1.2
Preparation and Characterization of an Insensitive RDX-Based Nanocomposite Explosive.
Hongwei Qiu 1 , Victor Stepanov 2 , Tsengming Chou 1 , Shuang Zhang 3 , Anthony Di Stasio 2 , Ashok Surapaneni 2 , Woo Lee 1 Show Abstract
1 CEMS, Stevens Institute of Tech, Hoboken, New Jersey, United States, 2 , U.S. Army - Armament Research, Development, and Engineering Center, Picatinny, New Jersey, United States, 3 , Visualization Sciences Group, Burlington, Massachusetts, United States
As accidental detonation of munitions can result in loss of life as well as tremendous cost and compromised capabilities, lots of research activities are currently aimed at producing explosives with reduced sensitivity. We report here the preparation and characterization of a cyclotrimethylenetrinitramine (RDX) explosive with significantly reduced shock sensitivity. The explosive was prepared using a spray drying based method, in which an acetone solution of RDX and a polymeric binder was spray dried to produce RDX nanocomposite granules, consisting of small RDX crystals (~0.1-1 μm) uniformly and discretely dispersed in the binder matrix. The pressed material exhibited a markedly lower shock sensitivity measured with the small scale gap test (SSGT). Due to the critical role of voids in determining the sensitivity of explosives, voids inside the explosive were characterized by focused ion beam (FIB) nanotomography to explore the origin of the shock insensitivity. Detailed structural parameters of voids, including size, shape, and spatial distribution were obtained. The results show that 90% of the captured voids are small (<400 nm). Combined with theoretical maximum density (TMD) data, it is implicitly shown that most of the porosity comes from voids less than 100 nm. We postulate that the low shock sensitivity is primarily linked to the absence of large voids. The novel production method developed in this work offers a simple and safe route to producing a wide range of insensitive explosive composites and realizing the immense potential of nanoenergetics.
10:15 AM - **Y1.3
Synthesis of Novel Tetraazapentalenes as High-Performance, Insensitive Energetic Materials.
Patrick Caruana 1 , Alfred Stern 1 Show Abstract
1 Indian Head Division, Naval Surface Warfare Center, Indian Head, Maryland, United States
Tetraazapentalenes are a class of high-nitrogen heterocycles with potential for use in Navy explosive and propellant formulations. The presentation will focus on the synthesis of pyrimidine-substituted tetraazapentalenes as derivatives of 2,4,8,10-tetranitrodibenzo-1,3a,4,6a-tetraazapentalene (TACOT), a molecule endowed with impressive thermal stability and insensitivity toward impact. These materials are expected to possess improved detonation parameters and Isp, higher heats of formation, and increased oxygen balance while retaining TACOT’s thermal stability. An emphasis will be placed on the optimization of reactions in the synthetic pathway and the characterization of novel intermediates via x-ray crystallography and spectroscopic methods. Specifically, nitration studies of diaminopyrimido-tetraazapentalenes will be described, and work toward the oxidation of novel amino heterocycles will be summarized. The presentation will also outline preliminary results on alternative pathways toward the target.
10:45 AM - Y1.4
Effect of Chemistry on the Performance of Calcium Disilicide Primers.
Paul Anderson 1 , Chris Csernica 1 , Mark Hash 2 , Joseph Hartvigsen 3 , Raymond Cutler 3 Show Abstract
1 , ARDEC, Picatinny, New Jersey, United States, 2 , Ervin Technologies, Tecumseh, Michigan, United States, 3 , Ceramatec, Inc., Salt Lake City, Utah, United States
Rotary atomization was used to synthesize spheres of CaSi2-based compositions in order to understand issues relative to primer performance for military applications. Elemental silicon and calcium were used to synthesize the line compound CaSi2 or the eutectic composition between CaSi2 and Si. Fe was added to form FeSi2 as a secondary phase in selected compositions. Rietveld analysis showed that CaSi2 polytypes in the synthesized materials consisted primarily of 6R, with less 3R and some hexagonal material. Synthesized materials had low surface areas (≈0.1 m2/g), but short milling times increased the surface area by an order of magnitude. Peak pressures, pressure rise time, and ignition voltage showed no significant differences between experimentally prepared samples and existing commercial samples. Stoichiometric CaSi2 performed as well as CaSi2-Si or CaSi2-FeSi2-Si mixtures. The military specification for calcium disilicide should be changed to reflect the broad chemistry which can be used for primer performance.A surprising result of this study was the performance of primers made with lower-surface area powders. These materials showed similar ignition voltage, pressure rise time, and peak performance to those made with higher surface area CaSi2. This suggests that a small fraction of fine particles is all that is necessary in order to start the exothermic reaction. Because the amount of primer increased when using the lower-surface area primers in the same volume, the change in particles shape affected the amount of primer added which may have confounded the results. While preparation of calcium disilicide by rotary atomization is more expensive than commercially available CaSi2 prepared by carbothermal reduction, such a methodology is uniquely suited for certain pyrotechnic and military specification compliant items. It is straightforward to control the purity required since high-purity Ca and Si are readily available, and spherical particles are produced, which are easily handled in air due to their low surface area and efficiently pack into the desired formulation producing a highly dense final product. The use of such materials in primers, however, requires some comminution in order to meet the current specifications.
Y2: Ultrafast Dynamics and Diagnostics
Monday PM, November 28, 2011
Room 309 (Hynes)
11:15 AM - **Y2.1
Dynamic Structural and Chemical Responses of Energetic Solids.
Haoyan Wei 1 Show Abstract
1 Department of Chemistry and Institute for Shock Physics, Washington State University, Pullman, Washington, United States
Understanding the dynamic response of solid under extreme conditions of pressure, temperature and strain rate is a fundamental scientific quest and a basic research need in materials science. Specifically, obtaining the atomistic/molecular level description of structural and chemical changes of solids under rapid heating and/or compression over a large temporal, spatial and energy range is critical to understanding the dynamics and mechanisms of mechanical deformation and fractures, thermal and mass diffusions, structural phase transitions, and chemical reactions. However, obtaining such real-time dynamic information in energetic solids across single-event exothermic processes such as combustions, deflagration, and detonation is a daunting challenge and requires time-resolved structural and chemical probes in micro- and nano-second time frames. In this paper, we will present recent experimental developments of time-resolved powder x-ray diffraction, laser spectroscopy, and high-speed microscopy, which enable us to determine structural and chemical evolutions during single-event exothermic metallic and intermetallic reactions. These time-resolved data provide insights into the mechanical deformation, fragmentation dynamics, energy impulse, phase transitions, chemical reactions, and constitutive properties of these reactive solids.* This work has been supported by the DTRA (HDTRA1-09-1-0041) and U.S. DHS under Award Number 2008-ST-061-ED0001.
11:45 AM - Y2.2
Chemical Pathways of Energy Release in Nitro Compounds: The 2-Nitro-2-Propyl Radical Intermediate.
Ryan Booth 1 , Laurie Butler 1 Show Abstract
1 Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, Illinois, United States
These studies investigate the unimolecular decomposition reactions of highly vibrationally excited radical intermediates in the combustion of energetic materials. Nitro-based energetic materials, such at TNAZ, RDX, HMX and FOX-7, have a strained ring with nitro functional groups and/or di-nitro substitution at one carbon atom. Their combustion certainly involves ring opening, loss of a nitro group, and nitro-nitrite isomerization, but the precise chemical mechanism is under debate. Our work generates an important radical intermediate in the proposed mechanisms, one with a nitro group and a radical center at the same C atom, and probes its competing unimolecular dissociation reactions under collision-free conditions. The experiments begin by generating a highly vibrationally excited 2-nitro-2-propyl radical from the photodissociation of 2-bromo-2-nitro-propane. Using a combination of velocity map imaging and crossed laser-molecular beam scattering, we probe the competition between two dissociation channels of the 2-nitro-2-propyl radical, C-NO2 fission and nitro-nitrite isomerization followed by a highly exothermic channel leading to acetone + NO. Detecting the products with VUV photoionization while also resolving their velocity distributions allows us to definitively identify these two processes. Electronic structure calculations of the relevant isomerization and dissociation transition states also characterize a HONO loss channel and a nearly isoenergetic channel producing OH radicals.
12:00 PM - Y2.3
Characterization of Voids and Microstructure in TATB-Based Explosives from 10 nm to 1 cm Using Synchrotron-Based USAXS and Microtomography.
Trevor Willey 1 , Lisa Lauderbach 1 , Franco Gagliardi 1 , Bruce Cunningham 1 , K. Thomas Lorenz 1 , Jonathan Lee 1 , Tony van Buuren 1 , George Overturf 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
Understanding initiation, detonation, and mechanical properties of highly insensitive explosives based on TATB (1,3,5-triamino-2,4,6-trinitrobenzene) requires a comprehensive understanding of the voids and microstructure, spanning length scales from nanometers to centimeters. We use a combination of synchrotron based ultra-small angle x-ray scattering (USAXS) and synchrotron-based microtomography. At smaller sizes, current hot-spot models suggest that voids with sizes between about 100 nm and few microns in these materials affect initiation and detonation properties. These are interrogated with USAXS. At larger sizes from microns to cm, synchrotron-based tomography allows quantitative determination of compositional variation. LX-17, a TATB-based polymer-bonded explosive (PBX), nominally is 7.5% binder and 92.5% TATB, however, LX-17 possesses a heterogeneous microstructure on the 1 mm scale, where binder rich boundaries (~8.3% binder, ~1% void) surround binder poor (~5.1%) and void rich (~2%) areas.Two insults, temperature cycling and compressive creep, cause very different microstructural damage. Temperature cycling, between -50 and 70C, causes an irreversible 1-2% volume expansion. In-situ USAXS observes the creation of voids from hundreds of nm to microns in size. Temperature cycling also causes some damage at larger length scales in the binder-poor areas of the explosive. Conversely, putting the explosive under a compressive load causes crack initiation and propagation at the binder-rich prill interfaces. These combined data are important to understanding microstructural mechanisms that affect mechanical properties, improving future TATB-based PBX materials. The results provide complete a comprehensive characterization of the structure from nanometers to centimeters and are also used as empirical input to computational models to determine how voids and microstructure affect shock response, initiation, and detonation properties.
12:15 PM - Y2.4
Development of Ultrafast Laser Spectroscopic Techniques to Study Fast Chemical Reactivity under Extreme Conditions of High Pressure and Temperature.
Alexander Goncharov 1 , Douglas Dalton 1 , Ryan McWilliams 1 2 , Mohammad Mahmood 2 Show Abstract
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States, 2 , Howard University, Washington, District of Columbia, United States
Here we address the need for a suite of ultrafast laser spectroscopic techniques to perform fast in situ chemical diagnostics of materials under extreme conditions of high pressure and high temperature. We report on new developments of a broadband optical spectroscopy technique (BBOS), which utilizes a broadband continuum generation in a photonic crystal fiber (PCF). Our tests show that this light source is sufficiently bright to perform optical spectroscopy measurements even in the presence of a very strong thermal radiation and optical fluorescence (e.g. in compressed O2). Moreover, this technique makes even single pulse measurements (e.g. concomitantly with laser driven shocks) feasible. The results on measurements of the optical spectra of oxygen and nitrogen in the fluid state will be presented at the meeting. Furthermore, we are in the process of developing of Coherent Anti-Stokes Raman spectroscopy (CARS) diagnostics using ultrashort (40 fs to 10 ps) laser pulses  and implementation of interferometric techniques utilizing short and chirped pulses with fast light detectors (e.g. streak cameras) to probe materials undergoing laser initiated shock and pulsed laser heating . 1. H. Kano and H. Hamaguchi, Appl. Phys. Lett. 85, 4298 (2004).2. A. F. Goncharov, J. A. Montoya, N. Subramanian, V. V. Struzhkin, A. Kolesnikov, M. Somayazulu, Russell J. Hemley, J. Synchrotron Rad. 16, 769 (2009).
12:30 PM - Y2.5
Investigation of Voids in Nanostructured RDX-Based Compositions Using Ultra-Small-Angle X-Ray Scattering.
Victor Stepanov 1 , Trevor Willey 2 , Jan Ilavsky 3 Show Abstract
1 , US Army, Picatinny Arsenal, New Jersey, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States
The nature of voids within novel cyclotrimethylene trinitramine (RDX)-based explosive nanocomposites was investigated. Voids are an important structural element due to their strong influence on properties such as sensitivity and performance. In order to probe the “sealed” voids, synchrotron-based Ultra-Small-Angle X-ray Scattering (USAXS) with Bonse-Hart configuration was employed. This powerful technique enabled probing voids with sizes ranging from ca. 1 nm to 3 microns with statistically meaningful sample sizes. Scattering data on three compositions with varying RDX crystal size, including 200 nm, 500 nm, and 2 microns, were measured. Modeling of the scattering intensity profiles, performed using the Maximum Entropy inversion routine, revealed bimodal, log-normal void size distributions for all samples. The mean void size was found to increase with the RDX crystal size and was found to be of similar dimensions to the RDX crystals. Majority of the porosity was due to voids larger than ca. 50 nm. The data also revealed information regarding the specific void/solid interfacial area, void shape, surface morphology, and porosity. Together with the a priori known crystal size distributions, these results constitute an unprecedentedly complete structural picture of this new class of energetic materials.AcknowledgementsChemMatCARS Sector 15 is principally supported by the National Science Foundation/Department of Energy under grant number NSF/CHE-0822838. Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
12:45 PM - Y2.6
Time-Resolved Emission Spectroscopy of Electrically Heated Energetic Ni/Al Laminates.
Christopher Morris 1 , Paul Wilkins 2 , Chadd May 2 , Timothy Weihs 3 Show Abstract
1 Sensors & Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 Department of Materials Science and Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
The nickel-aluminum (Ni/Al) intermetallic system is useful for a variety of reactive material applications, and reaction characteristics are well studied at the normal self-heating rates of 10^3 to 10^6 K/s. Recent experiments at 10^11 to 10^12 K/s have measured the kinetic energy of material ejected from the reaction zone, indicating additional kinetic energy from the reactive system despite high heating rates. In order to better probe reaction phenomena at these time scales, and determine the presence of expected elements and their temperatures, we report on emission spectroscopy of electrically heated, patterned Ni/Al bridge wires, time resolved over 350 ns through the use of a streak camera. We conducted these experiments in rough vacuum, but found the emission to be dominated by argon (Ar) and nitrogen (N) lines in addition to the expected emission of Al and Ni. Using spectral information of Ar, we analyzed the relative intensities of four Ar peaks between 425 and 455 nm, with respect to their expected Boltzmann distributions to yield temperatures as a function of time. These temperatures were 2.24–2.59 eV for Al samples, 2.93–3.27 eV for Ni/Al samples, and were within reasonable estimates of temperatures based on the measured electrical energy delivered to each device. Higher Ni/Al sample temperatures validated past measurements of increased kinetic energy and apparent formation reactions between Ni and Al. In the final paper, we will report on additional experiments with encapsulated bridge wires allowing better quantification of Al and Ni emission, but without the same level of interference from Ar and N. We will also look at shorter time scales, and correlate spectroscopic emission at early times with measured electrical input to compare phase change and expected initiation with similar phenomena in Ni/Al laminates at lower heating rates. These results will be important for new, energetically enhanced, high efficiency bridge wire applications, where shock initiation of subsequent energetic reactions may be accomplished with much less electrical energy than is currently required.
Y3: Detection, Imaging, and Sensing
Monday PM, November 28, 2011
Room 309 (Hynes)
2:30 PM - **Y3.1
Remote Explosives Detection (RED) by Infrared Photothermal Imaging.
Chris Kendziora 1 , Robert Furstenberg 1 , Michael Papantonakis 1 , Viet Nguyen 1 , R. Andrew McGill 1 Show Abstract
1 Code 6365, Functional Materials and Devices Section, Naval Research Laboratory, Washington, District of Columbia, United States
RED is a technique we have developed for stand-off detection of trace explosives using infrared (IR) photo-thermal imaging. RED incorporates compact IR quantum cascade lasers tuned to strong absorption bands and maybe used to illuminate explosives present as particles on a surface. An IR focal plane array is used to image the surface and detect any small increase in the thermal emission upon laser illumination. We have previously demonstrated the technique at several meters to 10’s of meters of stand-off distance indoors and in field tests, while operating the lasers below the eye-safe intensity limit (100 mW/cm2). Sensitivity to traces of explosives as small as a single nanogram grain have been detected. By varying the incident wavelength slightly, we can readily show selectivity between individual explosives such as TNT and RDX. Using a sequence of lasers at different wavelengths, we increase both sensitivity and selectivity. A complete detection protocol can be performed in a sub second time domain. More recently, RED has been used to emphasize measurements with cooled detectors and examine the utility of filtering the collected light signal which is rich in analyte information. A next generation RED system is being developed to take advantage of these more powerful features. This talk will include an overview of the approach and recent experimental results.References: R. Furstenberg et al. Applied Physics Letters 93, 224103 (2008), C. A. Kendziora et al.; Proc. of SPIE Vol. 7664 76641J-1 (2010).This research has been sponsored by ONR/NRL and the Office of the Secretary of Defense: Rapid Reaction Technology Office.
3:00 PM - Y3.2
Detection of Explosives by Hyper-Spectral Differential Reflectometry.
Thierry Dubroca 1 , Rolf Hummel 1 Show Abstract
1 material science, university of florida, Gainesville, Florida, United States
In the wake of the recent terrorist attacks, such as the 2008 Mumbai hotel explosion or the December 25th 2009 “underwear bomber”, our group has developed a technique (US patent #7368292) to apply differential reflective spectroscopy to the problem task of detecting explosives in order to detect terrorist threats. Briefly, light (200-500 nm) is shone on a surface such as a piece of luggage at an airport or a parcel at a courier distribution center. Upon reflection, the light is collected with a spectrometer combined with a camera. A computer processes the data and produces in turn a differential reflection spectrum taken between two adjacent areas of the surface. This differential technique is highly sensitive and provides spectroscopic data of explosives. As an example, 2,4,6, trinitrotoluene (TNT) displays strong and distinct features in differential reflectograms near 420 nm. Similar, but distinctly different features are observed for other explosives such as RDX, PETN or ANFO. Our detection system uses a two dimension detector (CCD camera) which provide spatial and spectroscopic information in each of the two dimensions. By scanning (involving fixed optical equipment and scanning moving bags or parcels on a conveyor belt), the surface to be surveyed the system provide the spatial location of the potential threat. We present in this paper how our detector works and how it is applied to the problem task of explosive screening for explosives at airports and mail sorting centers. Additionally, we will present the effect of the explosives morphology on the detection response. In particular we will evaluate the implication on the limit of detection of the instrument as well as discuss the sample morphology with respect to a realistic threat scenario. Finally, we will present our classification algorithm results which separate threats (explosives) versus non-threats materials under various background conditions.
3:15 PM - **Y3.3
Structural and Optical Property Tailoring of Black Silicon with fs-Laser Pulses.
Wolfgang Schade 1 Show Abstract
1 Institute for Energy Research and Physical Technologies, Clausthal University of Technology, Goslar Germany
Irradiating a planar silicon surface with femtosecond laser pulses under a sulfuric atmosphere creates first a structured surface featuring cones of up to 20 microns in height, and second a 0.1 – 1 µm thick layer of multi-crystalline silicon on theses cones containing up to 1 at.% sulfur acting as n-type dopant. Further, the sulfur establishes energy states within the band gap of silicon allowing for the absorption of infrared (IR) light with energies below the band gap energy of silicon. This black silicon process is distinguished by the fact that only one single laser process is required to tailor three material characteristics in on step: the surface structure, the doping and the light absorption. In this work we study different characteristics of black silicon and demonstrate resulting possible applications.We present black silicon absorption and internal quantum efficiency measurements for wavelengths reaching into the IR regime.Simulations based on ray tracing allow to calculate the refractive index n and the associated absorption coefficient of black silicon. n is shown to be continuous in substrate depth, as expected. It allows the prediction of light trapping characteristics.When manufacturing optoelectronic devices from black silicon, it is of great interest to keep charge carrier recombination small for not limiting the device performance. Recombination can be suppressed by passivation. We present first results of bulk passivation and of surface passivation layers on black silicon.For devices with a pn-junction the emitter characteristics are crucial. We investigate the emitter formed by the sulfur, and measure the emitter depth profile, surface concentration, and its lateral homogeneity.The sulfur can be built into the silicon lattice in different configurations, e.g.: ring-like or line-like, leading to different energy levels within the band gap of silicon and hence different absorption characteristics. The configuration of sulfur can be influenced by changing the temporal or spectral shape of the laser pulse. We shape laser pulses before using them to manufacture black silicon with different absorption characteristics.The IR absorption of black silicon enables a set of optoelectronic devices. For example, it is possible to convert the IR portion of the solar spectrum and thus black silicon can be used in novel photovoltaic devices. The absorption capabilities in the far IR launch black silicon as a promising substrate for thermophotovoltaics, where radiation from hot surfaces is converted into electric energy. We present a record efficiency solar cell based on laser processed black silicon without an additional emitter diffusion step and showing a nonzero quantum efficiency for incident light with energy below the silicon band gap. We demonstrate how the black silicon laser process can be integrated in standard industrial silicon solar cells to increase their efficiency.The next steps in our future work are to modify the atomic and molecular sulfur configuration in the silicon by coherent control. We expect that first the detrimental Shockley Read Hall recombination via the sulfur energy states in the band gap of silicon can be decreased, second the position of the sulfur energy levels and bands can be tailored and third, the absorption can be further increased over an even broader wavelength regime.This work is supported by the German Federal Ministry for the Environment, Nature Conservation and Reactor Safety (BMU) under project no. 0325157.
3:45 PM - Y3.4
Laser Trace Vaporization (LTV) of Trace Explosive Materials.
Michael Papantonakis 1 , Robert Furstenberg 1 , R. Andrew McGill 1 , Chris Kendziora 1 , Jakob Grober 1 , Viet Nguyen 1 Show Abstract
1 , US Naval Research Laboratory, Washington, District of Columbia, United States
The low vapor pressure of many energetic materials presents a challenge in the use of detection technologies for non-contact detection, which require a sample of the explosive to be presented directly into the instrument for analysis. We address this limitation by illuminating energetic materials including TNT and RDX with infrared lasers tuned to strong vibrational absorption bands to efficiently heat trace amounts present on various substrates and substantially increase their vapor signatures for direct detection without the need to swab surfaces for solid particles or to collect headspace vapors for extended time periods. The instantaneously generated vapor produced by Laser Trace Vaporization (LTV) can be detected by any number of detection techniques which can accommodate vapor sampling or spectroscopic analysis. Currently the testbed for LTV incorporates a tunable Quantum Cascade Laser (QCL) and an ion mobility spectrometer (IMS) used to validate the signal enhancements. The LTV technique works well with all tested substrates, though the thermal and spectroscopic properties of the substrate can influence the efficiency of the vaporization. However, by carefully optimizing the laser parameters, LTV has been demonstrated as a powerful technique able to quickly vaporize trace particles of explosives for rapid detection with IMS-based detectors. Computational results of laser heating of particles on surfaces along with experimental thermal kinetic measurements were used to optimize LTV laser irradiation parameters. In addition to a range of LTV results for different explosives and substrates, we explore the effects of wavelength-dependent heating on the sample and substrate.
Y4: Thermites and Nanoenergetics
Monday PM, November 28, 2011
Room 309 (Hynes)
4:15 PM - **Y4.1
Probing Reaction Dynamics of NanoThermites.
Michael Zachariah 1 Show Abstract
1 , University of Maryland, College Park, Maryland, United States
In this paper we discuss our current experiments and molecular modeling of how nanoscale metals and metal oxides react. We will discuss the importance of oxygen release from metal oxides on the ignition temperature and burn times as well as the role of the latent heat of oxidizer decomposition/melting. Using high temperature microscopy molecular dynamic modeling we show the importance of condensed state mass transfer in both moving fuel and oxidizer together and well as sintering effects which results in changing in particle size. The results question the idea that a decrease in particle size will necessarily lead to an enhancement in reactivity, since large amounts of sintering occurs early in the reaction, and alters the morphology. It is suggested that improvements in reactivity can be achieved by designing architectures to improve the interfacial contact upon sintering, as well as by selecting oxidizers based on their ability to liberate and transport oxygen in the condensed phase, while producing volatile species to assist in convective energy transport.
4:45 PM - Y4.2
Thermite Initiation Processes and Thresholds.
Curtis Johnson 1 , Kelvin Higa 1 , Thao Tran 2 , Rick Albro 2 Show Abstract
1 Research, NAVAIR, China Lake, California, United States, 2 Energetics Research, NAVAIR, China Lake, California, United States
The objectives of this work are to characterize thermite initiation processes, thresholds, and to develop thermite reactive trains, where a sensitive nanothermite composition ignites an insensitive micron thermite composition. Nanothermites, including Al/AgIO3, Al/Bi2O3, Al/MoO3, Al/Fe3O4, and Ti/AgIO3, were characterized for their ignition behavior by spark and resistively heated wire. Spark initiation was observed at energies down to about 9 microJoules, while hot wire initiation occurred at energies down to about 7 milliJoules. The hot wire results depended strongly on the diameter and length of the wire, indicating that the main limiting factor was the local temperature. Hot wire initiation energy for Al/Fe3O4 nanothermite was higher under argon than in air, indicating that air participates in the initiation process. The propagation rate of the Al/Fe3O4 nanothermite was about 100X slower than that of the other nanothermites. The relatively low reactivity of nano Al/Fe3O4 is attributed to the high thermal stability and high melting point of the oxidizer. Mixing of 90% Al/Fe3O4 nanothermite with 10% of a more sensitive, high-gas-producing nanothermite gave materials with the same sensitivity as the sensitive nanothermite. Thus, the mixture provides a safer sensitive nanothermite. Thermites with micron-scale ingredients were pressed into pellets and ignited with small amounts of nanothermite. For example, a 1.4 gram pellet of micron Al/Fe2O3 was ignited with 5 milligrams of nano Al/Fe3O4, which was initiated with a spark. Gas production of micron thermite compositions were reduced by adding the intermetallic former Ti/2B, or by adding excess iron. In both cases, a single hot mass was produced, while the pure micron Al/Fe2O3 produced a dispersion of iron particles. The dispersion of products from micron Al/Fe2O3 was also reduced by the mild confinement of placing the powder in an aluminum tube.
5:00 PM - **Y4.3
Inkjet Printing of Energetic Materials.
Alexander Tappan 1 , James Ball 1 , James Colovos 2 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Stanford University, Stanford, California, United States
We report work on utilizing inkjet printing as a technique to prepare samples of energetic materials with sub-millimeter dimensions. Inkjet printing is broadly applicable to any material that can be dispersed or dissolved in a suitable fluid. Utilizing a fluid as a carrier allows inherent processing safety advantages, results in homogenous deposition, and may be utilized to improve material properties through surface interactions, such as wetting and capillarity. A custom drop-on-demand inkjet printing system is utilized to deposit a dispersion of energetic material particles. The piezoelectric printhead expels a single droplet of fluid for each pulse delivered to it. A printhead with a 70 micron diameter orifice is utilized, which is large relative to typical inkjet printheads. The droplet size is typically on the order of the orifice size. A variety of energetic materials have been printed, with the bulk of the work conduced on two sub-micron thermites, consisting of Al/MoO3 and Al/Bi2O3. Aspects of the printing process, characterization of the printed material, and results on reaction (e.g., combustion) of energetic materials deposited by inkjet printing are presented.This work was supported by the Joint Department of Defense/Department of Energy Munitions Technology Development Program. * Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
5:30 PM - Y4.4
Activated Carbon Foams as Architectures for Nanoenergetic Composites: Optimization of Fabrication.
Alex Gash 1 , Margret Rakowsky 2 Show Abstract
1 Physical and LIfe Sciences, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of Chemistry, United States Air Force Academy, Colorado Springs, Colorado, United States
Activated acid-catalyzed carbon aerogels that posses extremely high surface area (up to ~3500 m2/g) and a hierarchial (macro-, and micro- porosity), are important new materials for study in a variety of areas. For example, the hierarchial structures provide advantages over mono-modal structures with high surface areas and diffusion efficiency and are interesting materials for catalyst supports and electrochemical devices. We have been examining the efficacy of these supports as nano-sized scaffolds that enable intimate mixtures of fuels and oxidizers for evaluation as energetic materials. This study details the results of various infiltration techniques for the deposition of oxidizers such as ammonium perchlorate and ammonium nitrate as well as oxidizer surrogate materials (ammonium sulfate and the ionic liquid tetra butyl ammonium benzoate) into the nano-porous network of fuel (carbon). Three deposition methods were principally employed: 1) Infiltration of a dissolved salt phase followed by solvent evaporation 2) Infiltration of a dissolved salt phase followed by solvent sublimation and 3), Melt infusion of an ionic liquid. The results of these studies as well as the characterization (SEM, pore size distribution, and thermal analysis) of resulting nano-composites will be reported and discussed.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
5:45 PM - Y4.5
Crystallization Kinetics of Vapor-Deposited Hexanitroazobenzene (HNAB) Films.
Robert Knepper 1 , Alexander Tappan 1 , Ryan Wixom 1 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Hexanitroazobenzene (HNAB) is an interesting material for microenergetic research on explosive behavior at sub-millimeter geometries due to its small critical thickness for detonation and its chemical stability at temperatures above its melting point, which allows for fast deposition rates. HNAB films fabricated using physical vapor deposition have been observed to have an amorphous structure, provided the substrate remains sufficiently cool during deposition. These amorphous films crystallize over a period of hours to weeks, depending on the ambient temperature. Several films were deposited to a thickness of ~ 100 microns and subjected to a variety of temperatures ranging from 30 – 75 degrees Celsius to observe crystallization behavior using time-lapse optical microscopy. Growth rates and crystallization times were analyzed to determine relevant kinetic parameters of the crystallization process. Variations in microstructure with crystallization temperature were characterized using scanning electron microscopy and atomic force microscopy.
M. Riad Manaa Lawrence Livermore National Laboratory
Choong-Shik Yoo Washington State University
Evan J. Reed Stanford University
Michael S. Strano Massachusetts Institute of Technology
Y5: High Energy Density and Storage
Tuesday AM, November 29, 2011
Room 309 (Hynes)
9:30 AM - Y5.1
Flash Ignition of Al Nanoparticles and Oxidation Mechanism.
Yuma Ohkura 1 , Pratap Rao 1 , Xiaolin Zheng 1 Show Abstract
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Aluminum nanoparticles (Al NPs), due to their high energy density, are important materials for propulsion systems, material synthesis and hydrogen generation. However, the oxidation mechanism of Al NPs at large heating rate remains inconclusive due to the lack of direct experimental evidence. Here, we studied the oxidation mechanism of Al NPs under large heating rate (on the order of 106 K/s or higher) by a simple flash ignition method, which uses a camera flash to ignite Al NPs. The flash ignition occurs when the Al NPs have suitable diameters and sufficient packing density to cause a temperature rise above their ignition temperatures. Importantly, transmission electron microscopy analysis reveals that the Al NPs are oxidized via the melt-dispersion mechanism, providing the first direct experimental evidence thereof. Finally, flash ignition is also applicable to the ignition of flammable gaseous, liquid and solid materials by the addition of Al NPs in lieu of sparks and hotwire igniters.
9:45 AM - Y5.2
High-Pressure Behavior of TAG--A Novel, Nitrogen-Rich Energetic Material.
Alexander Goncharov 1 , Ryan McWilliams 1 2 , Jennifer Ciezak-Jenkins 3 , Yasmin Kadry 4 , Vitali Prakapenka 5 , Mohammad Mahmood 2 Show Abstract
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States, 2 , Howard University, Washington, District of Columbia, United States, 3 , Army Research Laboratory , Aberdeen, Maryland, United States, 4 , University of Maryland, College Park, Maryland, United States, 5 CARS, University of Chicago , Chicago, Illinois, United States
Energetic materials are of interest in energy, mining, and defense applications. In the search for new energetic materials with improved properties, such as reduced environmental impact, a nitrogen-rich crystalline solid Triaminoguanidinium 1-methyl-5-nitriminotetrazolate (TAG), C3H12N12O2, has recently been synthesized (Klapötke et. al. 2008). We have studied the properties of TAG under static compression, and under reaction initiation at high pressure, using Raman and IR spectroscopy and x-ray diffraction. A complex structural deformation behavior is observed under compression, though the solid remains crystalline to at least 35 GPa. Laser initiation at 10-15 GPa reveals a rapid self-propagating reaction (deflagration) that consumes the sample, similar to other energetic materials such as nitromethane. Post-initiation products include crystalline molecular nitrogen, and nitrogen crystallites with regular defects.T. M. Klapotke, J. Stierstorfer, and A. U. Wallek, Chem. Mater. 20, 4519–4530 (2008).
10:00 AM - Y5.3
Developing High-Performance Energy Conversion Materials for Low-Grade Heat.
Yu Qiao 1 , Hyuck Lim 1 Show Abstract
1 Program of Mater. Sci. Eng., UCSD, La Jolla, California, United States
Harvesting and storing useful electricity from ambient thermal gradients/fluctuations, particularly low-grade heat (LGH) sources with temperature lower than 250 C, is an important research area. Usually, direct thermal energy conversion is achieved by using thermoelectric materials. Their energy conversion efficiencies, although already close to the upper limits, are still far from satisfactory. In order to meet the increasingly high functional requirements, new mechanisms must be investigated.Recently, a novel thermal-to-electric energy harvesting system based on enhanced interface charge transfer in nanoporous electrodes was developed by our team. With a relatively small temperature difference of only 40C, the output voltage could be 0.1-0.2 V. The energy density was ~2 J/g, much higher than that of many conventional thermoelectrics. This concept may open a new area of study for energy harvesting, conversion, and storage of LGH.
10:15 AM - Y5.4
Modeling of Early Stages of Formation of Poly-CO.
Iskander Batyrev 1 , William Mattson 1 , Betsy Rice 1 Show Abstract
1 , US Army Rsearch Laboratory, Aberdeen Proving Ground , Maryland, United States
We studied the early stages of polymerization of CO under pressure. We performed DFT simulations of 128 and 432 atom models. Structures of random networks found at zero temperature were used for equilibration at 100 K by employing first principles MD. We found that the polymerization begins at 7 - 8 GPa and slightly depends on the size of the model. It turned out that there are several metastable phases of the extended CO solid, corresponding to different compression pressures from 7-8 GPa to 15-18 GPa with different numbers of CO fragments, not connected to the random network. We also found that the transition to the phases is irreversible which results in hysteresis loops. Random network structures obtained, say, under 18 GPa could exist up to 3GPa, whereas compression to 3GPa results in the delta phase of CO crystal, with intact CO fragments and minor distortion of the cubic phase. To analyze the random structure fragments we calculated normal modes and IR intensity in the dipole approximation. Contributions from carbonyl and anhydride groups are identified and compared with experimental IR measurements.
10:30 AM - Y5.5
Broadband Dielectric Spectroscopy Study of the Solvent/Electrolyte-Soaked C-LiFePO4 Li-Ion Battery Electrode.
Cristian Perca 1 , Olivier Dubrunfaut 1 , Kalid-Ahmed Seid 2 , Jean-Claude Badot 3 , Stephane Levasseur 4 , D. Guyomard 2 , Bernard Lestriez 2 Show Abstract
1 , Laboratoire de Génie Electrique de Paris, SUPELEC, UPMC Univ Paris 06, Univ Paris-Sud, CNRS, France, Gif sur Yvette France, 2 , Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, France, Nantes France, 3 , Laboratoire de Chimie de la Matière Condensée de Paris, Chimie-Paris Tech (ENSCP), CNRS, France, Paris France, 4 , UMICORE Cobalt & Specialty Materials, Belgium, Bruxelles Belgium
The improvement of battery performance requires the rationale optimization of the composite electrode. Otherwise, the composite electrode formulation and processing have to be optimized by “trial and error” experiments. The development of “new tools”, i.e. experimental techniques as well as methodologies, is needed to understand the so-called composition architecture-properties and performance relationships.The improvement in electronic conductivity of the composite electrode is crucial toward high rate performance [1,2]. In a previous work , the broadband dielectric spectroscopy (BDS), from low (a few Hz) to microwave (a few GHz) frequencies, has been used to study composite electrodes. It has been shown that this technique is very sensitive to the different scales of the electrode architecture involved in the electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents.Most studies are focused on the electrode conductivity by dc or BDS or on the electrical/electrochemical behaviour of the whole battery, by the classical electrochemical impedance spectroscopy for example. The influence of the solvent/electrolyte components on the electrical behaviour of the electrode is not well known. This influence can be originated in the adsorption of the dipolar molecules or Li ions, and thus creating an electric field on the surface of the solid. We can also imagine that these species can be adsorbed on the cluster junctions inducing modifications on the electronic transport between clusters.In this work, BDS is used to study LiFePO4-based composite electrodes which are soaked with different (polar and nonpolar liquids and the Li+ electrolyte. Our aim is to study a system similar to the one found in working Li-ion batteries. We are thus progressively increasing the complexity of our system, by successively adding the various solvents (DMC, DMC-EC, 3DMC-EC…) and the electrolyte. Firstly, the electrode is soaked in a nonpolar liquid. Polar liquids/solvents are subsequently used, and the corresponding influence on the electrode is studied. In the final stages, the Li+ ion/solvent is used, in different concentrations, and its influence on the electrode and the solvent is studied. For each sample, complex permittivity and resistivity diagrams have been plotted. The contributions, which have been evidenced by spectral decomposition, were compared with those observed in the dry electrode.References1. C. Fongy, A-C. Gaillot, S. Jouanneau, D. Guyomard and B. Lestriez, J. Electrochem. Soc., 2010, 157, A885.2. C. Fongy, S. Jouanneau, D. Guyomard, JC. Badot, B. Lestriez, J. Electrochem. Soc., 2010, 157, A1347.3. J.C. Badot, E. Ligneel, O. Dubrunfaut, D. Guyomard, and B. Lestriez, Adv. Funct. Mater. 2009, 19, 2749.Financial funding from the ANR program n° ANR-09-STOCKE-02-01 is acknowledged.
Y6: Initiation, Ignition, and Detonation I
Tuesday PM, November 29, 2011
Room 309 (Hynes)
11:15 AM - **Y6.1
Experiments Probing Fundamental Mechanisms of Energetic Material Initiation and Ignition.
Christopher Berg 1 , Alexei Lagutchev 1 , Hiroki Fujiwara 1 , Kathryn Brown 1 , Yuanxi Fu 1 , Dana Dlott 1 Show Abstract
1 School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
When a shock of sufficient strength passes through an energetic material, initiation followed by ignition can occur. Initiation refers to the onset of widespread chemical reactions and for stable secondary explosives, initiation is an endothermic process and it may be unimolecular and may occur on the picosecond time scale. Ignition, which may occur on the nanosecond time scale, refers to the onset of strongly exothermic reactions and these cannot be unimolecular, since energy is released only when two fragments combine to form a strong chemical bond. To study these processes in detail, we have developed two experimental techniques. For initiation studies, a monolayer of molecules containing functionalities present in energetic materials is subjected to femtosecond pulse shock compression and temperature jump while infrared is used to probe chemical changes. For ignition studies, a layer a few microns thick of energetic materials is impacted by a laser-driven flyer plate generating a shock 10 nanoseconds in duration while the materials are probed by various spectroscopic techniques.This material is based on work supported by the Air Force Office of Scientific Research through contract FA9550-09-1-0163, the Army Research Office through contract W911NF-10-0072 and the Office of Naval Research through contract N00014-11-1-0418.
11:45 AM - **Y6.2
Shock Initiation Mechanisms and Relative Sensitivities of Homogeneous and Heterogeneous Explosives.
Dana Dattelbaum 1 , Stephen Sheffield 1 , Virginia Manner 1 , David Stahl 1 , Lloyd Gibson 1 Show Abstract
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Homogeneous (liquid) and heterogeneous (composite) explosives exhibit fundamentally different initiation mechanisms under temporally-sustained shock compression conditions. Liquid explosives initiate via a thermal explosion mechanism. The initiation sensitivities and mechanistic details have been investigated for several liquid explosives with different chemical structures, including nitromethane, FEFO, and hydrogen peroxide/H2O solutions. The liquids have been found to be highly state sensitive and less sensitive compared with many plastic-bonded explosives. In heterogeneous explosives, by contrast, shock initiation is believed to occur through the localization of energy in regions of temperature and pressure called “hot spots.” To gain insights into the critical hot spot features influencing energetic materials initiation, well-defined micron-scale particles have been intentionally introduced into the homogeneous explosive nitromethane (NM). Two types of potential hot spot origins have been examined - shock impedance mismatches using solid silica beads, and porosity using hollow glass microballoons – as well as their sizes and inter-particle separations. We present the results of several series of gas gun-driven plate impact experiments on NM/particle mixtures with well-controlled shock inputs. Detailed insights into the nature of the reactive flow during the build-up to detonation have been obtained from the response of in situ electromagnetic gauges. Microballoons (porosity) were found to be more effective than solid particles (shock impedance mismatches) at producing hot spot-driven flow at the same size and number density. We have further found a balance between thermal explosion-driven and hot spot-driven initiation depending on the size and number density of the particles.
12:15 PM - Y6.3
The Detonation Properties of Combined Effects Explosives.
Paul Anderson 1 , Paula Cook 1 , Wendy Hummers 1 Show Abstract
1 , US Army RDECOM-ARDEC, Picatinny Arsenal, New Jersey, United States
In development of new explosives, it is often necessary to balance a number of attributes in performance while certain formulation constraints exist. Picatinny Arsenal utilizes statistical design of experiments (DOX) to quickly optimize formulations and provide the optimal processing, performance, and insensitivity. During the development of metal-loaded explosives designed for enhanced blast, it was discovered that upon proper formulation, all of the aluminum additive participates early in the detonation event. This results in extremely high Gurney energies equivalent to LX-14 and PBXN-5 but with lower loading of nitramines. The early aluminum oxidation can be described by Eigenvalue type detonation, where the fully reacted Hugoniot of the condensed phase aluminum oxide and explosive products lies below the unreacted aluminum Hunoniot. Such an analysis describes fully the agreement of aluminum consumption by 7 volume expansions from 1-inch copper cylinder expansion tests and an analytic cylinder model, as well as detonation velocity/plate dent tests. With the early reaction of aluminum also comes a shift in the gaseous reaction products to higher enthalpy species such as CO and H2, leading to further augmentation of blast. Thus, both the mechanical energy (for fragmentation or “metal pushing”) and blast (for structural targets) are available in a single explosive fill. This provides the capability for combined metal pushing and blast in a single explosive that was not previously possible. The development of such explosives and the importance of modern statistical design of experiments will be shared.
12:30 PM - Y6.4
In Situ Remediation of Hydrogen Fluoride during a Detonation Event.
Kelley Caflin 1 , Paul Anderson 1 Show Abstract
1 , RDECOM ARDEC, Picatinny Arsenal, New Jersey, United States
Hydrogen fluoride (HF) is a known product from the combustion or detonation of explosives formulated with fluoropolymer binder systems. This presents the user with elevated risk levels, particularly during unintended combustion events or detonations in constrained environments. In an effort to remediate the production of HF, calcium disilicide was added to explosive formulations in an effort to decrease the amount of HF formed. First, VitonA/calcium disilicide mixtures were made and the thermal decomposition characteristics studied using thermal gravimetric/differential thermal analysis. The activation energy ranged from approximately 145-190 kJ/mol, indicative of C-F scission in the Viton A binder prior to calcium fluoride formation. An energetic formulation was made which consisted of approximately a 5/3 mass ratio of VitonA/CaSi2. Combustion calorimetry in oxygen and air and subsequent analysis of the residues using x-ray diffraction (XRD) and energy dispersive x-ray analysis (EDS) revealed that calcium fluoride formed. The amount of HF reduced was determined by trapping off gases in a cooling loop, rinsing into water, and analysis in anion exchange chromatography. Upon introduction of calcium disilicide into the explosive formulation, a ~30% decrease in HF formation was observed along with appearance of CaF2 and free Si in the residue. Such products are consistent with the mechanism following a general decomposition path of 2F + CaSi2 → CaF2+2Si. The same formulation was detonated, and upon product analysis it was determined the decomposition path followed nearly the same route with a net decrease in HF formation, but with a portion of the silicon oxidizing slightly further to SiO2.
12:45 PM - Y6.5
Microwave-Induced Thermal Transitions in HMX for Decomposition Kinetic Analysis.
Amanda Duque 1 , W. Lee Perry 1 , Laura Smilowitz 1 , Bryan Henson 1 Show Abstract
1 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Microwave (MW) irradiation offers the unique ability to uniformly heat material at extremely high rates while maintaining a uniform temperature distribution. In contrast, conventional external heating methods are inherently transport limited and cause a low heating rate and large temperature gradients. We apply fast MW heating to the study of the decomposition kinetics of the secondary high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). Because HMX alone is MW inactive, nanocomposites comprised of an HMX-binder system doped with carbon nanotubes (CNTs) have been fabricated and the dielectric properties measured. The dielectric properties of a material are an intrinsic value that describes the expected MW-materials interaction and predicted heating response. Obtaining dynamic temperature measurements of the HMX composite under MW exposure is essential for accurate analysis of the decomposition kinetics; we utilize a fiber-optic pyrometer to make single-point measurements, which minimizes perturbations of the electric field. We show that fiber-optic temperature measurement techniques may be effectively interfaced with a microwave resonator, and can reproducibly be correlated to the amount of MW energy absorbed in the sample.Beginning at 160 °C, HMX undergoes a β- to δ- conformational phase transformation; the δ-form of HMX produces a second-harmonic generation (SHG) at 532 nm when irradiated with 1064 nm laser light. Detection of the SHG intensity, and thus mole fraction of δ-HMX present, as a function of temperature is a useful probe for describing the HMX decomposition kinetics in a fast regime (10-2 s). The incorporation of MWs with SHG detection and temperature measurement will aid in building a more complete model of HMX decomposition and understanding the role that the crystalline phases play in a kinetic regime that has been sparsely investigated.
Y7: Thermodynamic, Chemical, and Mechanical Properties
Tuesday PM, November 29, 2011
Room 309 (Hynes)
2:30 PM - **Y7.1
Future Energetic-Materials Basic Research.
Suhithi Peiris 1 Show Abstract
1 RD-BA Directorate, Defense Threat Reduction Agency, Fort Belvoir, Virginia, United States
Energetic materials with fast energy release have been utilized in rockets and weapons for many centuries. New weapon technologies designed for defeat of biological agents and for defeat of hard or deeply buried targets such as buildings, tunnels and caves are being developed at the Defense Threat Reduction Agency (DTRA). The DTRA Basic Research program seeks better energetic materials for future use in these weapons.Energetic materials react to yield heat and gaseous reaction products, resulting in high temperatures and high pressures. Inherently, materials with fast energy release are metastable, often with positive heats of formation, making them extremely sensitive to friction, heat, etc. Therefore, future energetic materials must not only have higher energy density with high release rates, but also controllable energy release or insensitivity to external stimuli. As seen by efforts over the past 50+ years, synthesis approaches within traditional C, H, O, N chemistry will likely yield only modest increases in energy density. Non-traditional approaches using novel types of materials and process hold more promise to achieve much higher energy densities. For instance, metal and/or organic ingredients that are polymerized in block co-polymer-like configurations, or prepared in composites of stacked ultrathin single-crystal sheets, or self-assembled into larger three-dimensional fully dense crystalline composites, etc. Future energetics may also be designed and built similar to metamaterials, with various fuel-oxidizer composite components that have the necessary shock-wave refracting indices to produce and focus energy. Further, because of the fast kinetics of energetic material reactions, the initiation, reaction to detonation or combustion, gas production and associated turbulence, etc. are still not well characterized with the necessary time resolution, at the appropriate and high-pressure high-temperature conditions. Future energetic materials need experimental and numerical investigation so that we can model and simulate their performance with purely science-based models, and thereby design materials with reproducible high energy density and controllable fast energy release.
3:00 PM - Y7.2
Nanoporous Carbons as Selective Adsorbents for Energetic Molecules.
Anna Merritt 1 , Ramakrishnan Rajagopalan 2 , Nirupam Trivedi 1 Show Abstract
1 , Naval Air Warfare Center Weapons Division - China Lake, China Lake, California, United States, 2 , The Pennsylvania State University, University Park, Pennsylvania, United States
Nanoporous carbons (NPCs) are especially attractive adsorbent materials due to their high internal surface area, inert chemical nature, mechanical robustness and easy rengenerability via the application of heat, pressure, electrical and/or chemical gradients. Separation of adsorbates on NPC can be achieved provided that the adsorbate possess sufficiently dissimilar features in terms of size, shape or chemical affinity. Industrially important separation processes such as small gas molecule separation, volatile organic compound recovery, sulfur gas and heavy metals trapping have been extensively demonstrated with carbon adsorbents. In contrast, the selective adsorption of energetic molecules on carbon has received far less attention.In this work, the ability of NPC adsorbents to display size/shape selective adsorption behavior for energetic molecules was examined. Carbon adsorbents with variable pore size and pore volume were prepared from the pyrolysis of polymeric precursors. Liquid nitrate esters including triethylene glycol dinitrate (TEGDN), N-n-butyl-N-(-2-nitroxyethyl) nitramine (BuNENA) and butanetriol trinitrate (BTTN) were then sorbed onto the carbon structure. The amount of adsorbate and the adsorbate binding strength were observed by thermal techniques such as differential scanning calorimetry and thermogravimetric analysis. It was found that nanoporous carbons display size/shape selectivity for nitrate ester molecules. This study shows that careful control over the structure of the carbon structure can endow adsorbents with selectivity for energetic molecules; this observation could have important implications for the future development of advanced explosive sensing devices.
3:15 PM - Y7.3
Relationship between Local Temperature Fluctuations and Molecular Conformational Stability in a-RDX Crystals.
Nithin Mathew 1 , Catalin Picu 1 Show Abstract
1 Department of Mechanical Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
The RDX molecule has four conformations denoted as Caaa, Caae, Caee and Ceee, of which Caae is the conformer stabilized at room temperature in the a-RDX crystalsubjected to atmospheric pressure. The only other conformer stabilized in the crystal is Caee and this occurs when the crystal is strained. The concentration of Caee depends on strain and temperature. These conformers interact elastically and electrostatically, which leads to their spatial clustering. Furthermore, the transition between Caae and Caee is a stochastic process characterized by temporal correlations. This is due to the field-mediated spatial interaction of conformers. Fluctuations in theintra-molecular effective temperature correlate with conformational transitions; the Caee molecule having lower intra-kinetic energy immediately after a Caae to Caee transition, and the Caae molecule having higher intra-kinetic energy after a Caee to Caae transition.
Y8: Initiation, Ignition, and Detonation II
Tuesday PM, November 29, 2011
Room 309 (Hynes)
4:00 PM - Y8.1
A Study of the Ignition Threshold in Reactive Materials.
Gregory Fritz 1 , Stephen Spey 1 , Timothy Weihs 1 Show Abstract
1 Materials Science and Enginnering, Johns Hopkins University, Baltimore, Maryland, United States
Ignition thresholds for reactive materials are known to vary within a given material system, in part due to the fact that the rate of heat losses away from the ignition volume varies dramatically between ignition methods. Techniques with very localized heating, such as laser or spark ignition, can have very high volumetric heat losses and therefore require a higher energy density for ignition compared to methods with large ignition volumes and much smaller heat losses. Here we present a mathematical model which accounts for heat losses during the ignition process and can be used to predict the relationship between microstructural/geometrical parameters and ignition thresholds. The model is validated using Ni/Al nanolaminate foils as a model system for a variety of test techniques. Ignition temperatures below 300 oC are measured for uniform heating techniques with large ignition volumes demonstrating that ignition can occur in the solid state. An activation energy of 77.6 ± 1.3 kJ/mol is quantified using an uniform heating technique while numerical modeling predicts a diffusion pre-exponential coefficient of 5.58x10^-9 m2/s for the Ni/Al system. The calculated values will be compared to literature values and numerical predictions of temperature-time profiles for the ignition process will be compared to measured data.
4:15 PM - **Y8.2
Multiscale Simulation of Hot Spot Ignition.
Laurence Fried 1 , Fady Najjar 1 , Michael Howard 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
High explosive shock sensitivity is controlled by a combination of mechanical response, thermal properties, and chemical properties. How these properties interplay in realistic condensed energetic materials is not well understood. In this paper, we use a multiscale approach to achieve a realistic simulation of hot spot (void) ignition in a single crystal of the explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The smallest length scale (< 10 nm) of the multiscale model was treated quantum mechanically. We have conducted multiple simulations of the decomposition of the explosive TATB using density functional tight binding molecular dynamics (DFTB-MD). Nanoscale continuum simulations were performed of void ignition using the ALE3D hydrodynamic/thermal/chemical code.
4:45 PM - Y8.3
Accurate Rankine-Hugoniot Relationships for Molecular Crystal Explosives Calculated Using Density Functional Theory Based Molecular Dynamics.
Ann Mattsson 1 , Ryan Wixom 2 , Thomas Mattsson 3 Show Abstract
1 Computational Shock and Multiphysics MS 1322, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Energetics Characterization MS 1455, Sandia National Laboratories, Albuquerque, New Mexico, United States, 3 HEDP Theory MS 1189, Sandia National Laboratories, Albuquerque, New Mexico, United States
In a broad range of research areas, Density Functional Theory (DFT) has become a requisite tool for understanding the behavior of materials. The ability to perform high-fidelity calculations is especially important for cases where experiments are impossible, dangerous, and/or prohibitively expensive to perform. For molecular crystals explosives, successful application of DFT has been hampered by an inability to correctly describe the van der Waals’ dominated equilibrium state. However, we have explored a way of bypassing this problem by using the Armiento-Mattsson 2005 (AM05) exchange-correlation functional and focusing on the compressed state. The AM05 functional is known to be highly accurate for a wide range of solids and is unique because it contains no van der Waals’ attraction. We have used AM05 DFT based molecular dynamics to calculate the unreacted principle Hugoniot for several important molecular crystal explosives: PETN, HNS, CL-20, and TATB. We are also using this technique to investigate reactions occurring in the shock-compressed material. We will discuss our approach, the advantages of using AM05, and report our newly generated equations of state for these materials, making comparisons to experimental data where it exists. Along with enhancing our fundamental understanding of the shock response of explosives, our results fill critical gaps in data needed by design engineers and will greatly improve the accuracy of hydrocode simulations involving these materials. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
5:00 PM - Y8.4
Deformation and Fragmentation Mechanisms Leading to Ignition of Reactive Case Materials
William Wilson 1 , Kibong Kim 2 , Fan Zhang 3 , Craig Watry 4 , Mary Brown 4 Show Abstract
1 , Defense Threat Reduction Agency, Fort Belvoir, Virginia, United States, 2 , AER, Inc., Vienna, Virginia, United States, 3 , Defence Research and Development Canada, Suffield, Alberta, Canada, 4 , Applied Research Associates, Inc., Albuquerque, New Mexico, United States
In recent years, there has been growing interest in the use of energetic structural materials to replace inert materials in weapon systems, for instance, use of reactive materials to replace warhead steel cases. Several researchers have shown that when inert cases are replaced by reactive structural materials the blast pressure and impulse produced by these devices can be enhanced. While the blast pressure histories clearly show that enhancements result, details of the timing of the energy release necessary to produce the enhancements are not clear from such records. It is now widely assumed that pressure enhancements from reactive cases must be mainly or entirely due to rapid reaction of the case materials, including combustion with detonation products and air. More fundamentally, it is not clear from many of these tests what the detailed mechanisms are which lead to initiation of reaction of the case materials. In this work, we have conducted experimental work to delineate the deformation processes in metallic reactive material cases that lead to ignition of combustion. Two classes of material cases have been studied: solid metal alloys, and pressed metallic powder mixtures. The response of these materials under explosive loading differs in ways which affect the extent and the timing of reaction initiation. At least two very different modes of ignition have been identified, and which one of these dominates is dependant upon the material class used. High speed photography of case fragmentation, fragment acceleration, and case material impact on surrounding structure shows details of the various modes of ignition. Analysis of high fidelity pressure-time histories is also used to estimate the timing of case material ignition, to help differentiate between likely ignition modes. The high fidelity hydracode SHAMRC has also been used to further clarify the role of case fragmentation and material deformation in the ignition process.
5:15 PM - Y8.5
Initiation and Decomposition of Tetrazole Containing Green Energetic Materials.
Nicholas Piekiel 1 , Richard Cavicchi 2 , Michael Zachariah 1 2 Show Abstract
1 , University of Maryland, College Park, College Park, Maryland, United States, 2 , National Institute of Standards of Technology, Gaithersburg, Maryland, United States
Green energetic materials have recently gained significant interest as an alternative for traditional organic energetics, as they produce relatively non-toxic reaction products while maintaining a similar level of reactivity. With the use of a Temperature-Jump/Time-of-Flight Mass Spectrometer (T-jump/TOFMS), capable of heating rates up to 10^6 K/s and a characteristic sampling time of 100 µs, the initiation and decomposition of these materials has been examined. The samples include 5-amino-1-methyl-1H-tetrazolium dinitramide (MeHAT_DN), 1,5-diamino-4-methyl-1H-tetrazolium dinitramide (MeDAT_DN), 1,5-diamino-1H-tetrazolium nitrate (DAT_N), 1,5-diamino-4-methyl-1H-tetrazolium azide (MeDAT_N3), and 5-aminotetrazolium dinitramide (HAT_DN), which were produced by the Klapötke group of the Ludwig-Maximilian University of Munich. Each material has a structural commonality of a tetrazole containing cation, paired with a variety of anion configurations. Since the tetrazole structure is a large part of each of these materials, the neutral 5-amino-1H-tetrazole (5-AT) was also tested to compare the decomposition between neutral and ionic species. Under rapid heating conditions, two competing breakdown mechanisms are observed for the cation’s tetrazole ring, one which forms molecular nitrogen, the other hydrogen azide. These mechanisms do not appear to have any dependence on the temperature of the reaction, but rather on the location of functional groups around the tetrazole ring. When functional groups are placed in a symmetric fashion around the tetrazole ring, N2 is a primary reaction product, but if the groups are asymmetric, HN3 is formed. For some materials, these findings differ substantially from previous studies at slow heating rates. There are also multiple reaction pathways for the dinitramide anion; a low temperature pathway forms NO2 and a high temperature pathway forms N2O, which is consistent with previous studies. In a complimentary study several of these materials were tested on a micro-DSC device developed at the National Institute of Standards and Technology (NIST). Due to its small size, this system allows for rapid heating of samples and sensitive detection of thermal events. A varied heating rate experiment was performed to determine an activation energy for each material varying from 41-74 kJ/mol, which was significantly lower than previously reported values. This further indicates that under rapid heating conditions, different mechanistic processes are at play.
5:30 PM - Y8.6
Characterizing Ignition and Growth Phenomena for Thin-Pulse Initiation.
Ryan Wixom 1 , Eric Welle 2 , Evan Dudley 1 Show Abstract
1 Energetics Characterization, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Air Force Research Laboratory/Munitions Directorate/Fuze Branch, Eglin AFB, Florida, United States
Alfred Nobel’s invention of dynamite was probably the first demonstration of the relationship between porosity and initiation sensitivity of an explosive. In the years since, it has been explicitly shown that microscopic bubbles, collapsing under shock, are responsible for the incredible ignition sensitivity of nitroglycerine. This link has also been made for other transparent liquid and gel explosives by directly imaging pore collapse under shock. It has been proposed that shock-pore interactions are also potential nuclei for initiation in consolidated molecular crystal explosives. Unfortunately, it is difficult if not impossible to perform analogous experiments for opaque or translucent polycrystalline solids. Following those same concepts, we are using new microstructural characterization techniques (e.g. ion-beam cross-sectioning and nanotomography) to study the link between pellet porosity and ignition and growth phenomena, with specific focus on the thin-pulse initiation of hexanitrostilbene (HNS). In addition to microstructural characterization we have pursued extensive performance testing, including threshold, mini-wedge tests, and cutback studies. These data are analyzed in the context of critical energy fluence vs. critical specific energy, which provides easy to understand design criteria and can also be used to parameterize ignition and growth models for hydrocode simulations.Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
5:45 PM - Y8.7
Heat-Initiated Oxidation of Aluminum Nanoparticles.
Richard Clark 1 , Weiqiang Wang 1 , Ken-ichi Nomura 1 , Rajiv Kalia 1 , Aiichiro Nakano 1 , Priya Vashishta 1 Show Abstract
1 CACS (Collaboratory of Advanced Compting and Simulation), Department of Physics, University of Southern California, Los Angeles, California, United States
Multimillion-atom reactive molecular dynamics simulations were used to investigate the interplay of mechanisms which control oxidation in aluminum nanoparticles due to heat initiation. The simulation results reveal three stages of reaction: (1) confined burning, (2) onset of deformation, and (3) onset of small cluster ejections. The first stage of the reaction is localized primarily at the core-shell boundary, where oxidation reactions result in strong local heating and increased migration of oxygen from the shell into the core. When the local temperature rises above the melting point of alumina (T=2330K), the melting of the shell allows deformation of the overall particle and an increase in heat production. Finally, once the particle temperature exceeded the threshold temperature of 2800-3000 K, ejection of small aluminum-rich clusters occurred from the outside of the shell. The underlying mechanisms were explored using global and radial statistical analysis, as well as developed visualization techniques and localized fragment analysis. The three-stage reaction mechanism found here provides insight into the controlling factors of aluminum nanoparticle oxidation and detonation, topics of considerable importance in the energetic materials community.
Y9: Poster Session
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - Y9.10
Directed Assembly of Energetic Materials with Micro-Engineered Architectures.
Kyle Sullivan 1 , Cheng Zhu 1 , Joshua Kuntz 1 , Eric Duoss 1 , Alex Gash 1 , David Kolesky 2 , Douglas Tanaka 2 , Jennifer Lewis 2 Show Abstract
1 , Lawrence Livermore National Lab, Livermore, California, United States, 2 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Direct ink writing (DIW) has successfully been used in combination with electrophoretic deposition (EPD) as a means to synthesize micro-engineered architectures of energetic materials. Patterns of planar and 3D electrode lattices are printed onto arbitrary substrates, and EPD is then used to deposit thermite materials onto the surface, or to infill the interconnected pores. This combination of techniques allows for unique mechanistic investigations of the fuel / oxidizer ignition and reaction in thermites, and has a direct application for microenergetic systems which would benefit from controlled placement of the energetic material. Furthermore, this scalable capability will allow for bottom-up assembly of energetic systems with micro-engineered tailoring. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Release # LLNL-ABS-488551
9:00 PM - Y9.11
The Role of Metal Oxides in the Condensed Phase Initiation of Nanothermites.
Nicholas Piekiel 1 , Kyle Sullivan 1 , Lei Zhou 1 , Snehaunshu Chowdhury 1 , Stephen Kelly 2 , Todd Hufnagel 2 , Kamel Fezzaa 3 , Michael Zachariah 1 Show Abstract
1 , University of Maryland, College Park, College Park, Maryland, United States, 2 , Johns Hopkins University, Baltimore, Maryland, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States
This work is a culmination of several corresponding studies designed to probe the initiation and decomposition of aluminum based nanothermites. The main diagnostic tool is a Temperature-Jump/Time-of-Flight Mass Spectrometer (T-Jump/TOFMS), which uses a filament heating method capable of very high heating rates of up to 10^6 K/s, while simultaneously recording spectra at a time resolution of 100 µs. Nanothermites of Al/CuO, Al/Fe2O3, Al/WO3, and Al/Bi2O3 were tested with this system along with the neat Al and metal oxide nanopowders. After heating under vacuum, comparison of the time-resolved decomposition profiles of Al/Bi2O3 and neat Bi2O3 nanopowder revealed that the nanothermite ignited prior to the production of a gaseous oxidizer, indicating a condensed phase initiation reaction. This mechanism is unclear for the other nanothermites tested and prompted further investigation of several carbon nanocomposites, C/Bi2O3, C/CuO, and C/Fe2O3 as, unlike aluminum, carbon will remain in the solid phase within the temperature regime of our experiments. Each carbon nanocomposite demonstrated a similar condensed phase reaction as Al/Bi2O3 indicating that each oxidizer is capable of initiating the reaction in this manner. A complimentary study was also performed using a high heating rate TEM grid to observe the morphology of nanothermites before and after rapid heating. This system probed the behavior of individual nanoparticles and again provided evidence for condensed state reactions. For Al/Bi2O3, the oxide failed to react with nearby (not in contact) Al, but underwent a significant reaction with the underlying carbon layer of the TEM grid. WO3 also failed to react with nearby Al, but underwent substantial morphological changes where Al and WO3 were in contact. From these findings we propose a reactive sintering mechanism as a generic model for the initiation of nanothermite reactions. This model was further supported by an experiment at Argonne National Laboratory’s Advanced Photon Source, using high speed phase contrast imaging to view the nanothermite reactions. This x-ray imaging method allowed for viewing of early condensed state reactions prior to ignition.
9:00 PM - Y9.13
Embossing of Crystalline Organic Thin Film Using Micro-Contact Printing: Applications on Energetic Materials.
Xin Zhang 1 , Gengxin Zhang 1 , Yen-Chih Liao 1 , Brandon Weeks 1 Show Abstract
1 Chemical Engineering, Texas Tech University, Lubbock, Texas, United States
In energetic materials research, preparation of micro/nanoscale patterning may improve material performance, such as thermal stability, friction sensitivity and explosive output, because the performance depends strongly on micro-structure, such as particle size distribution, surface area, void volume within the energetic material. Here we report a novel top-down fabrication method for embossing of crystalline organic energetic materials through cationic surfactants combined with micro-contact printing (μCP). The method employed uses simple experimental procedures, has high efficiency and can be used to produce patterns with vertical dimensions from 100nm up to 3um. By applying different patterns this technique provides a new manner in studying the mechanisms of initiation and propagation of micro/nano-organic energetic materials.
9:00 PM - Y9.14
Study of Dislocations in RDX Using Atomistic Simulations.
Nithin Mathew 1 , Catalin Picu 1 Show Abstract
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Dislocation-mediated plastic deformation is recognized as a mechanism for hot-spot formation and detonation in energetic materials. We report on the dislocation core structure and Peierls stress in RDX, for edge and screw configurations and for various slip-systems. These are obtained by atomistic simulations and by using the Peierls-Nabarro model, with generalized-stacking fault energies obtained from atomistic simulations. The objective is to identify the slip systems (and associated core configurations) with the smallest barrier for dislocation motion. The effect of non-Smith stresses on the core structure and the Peierls stress are also investigated.
9:00 PM - Y9.15
Size Dependence of the Dynamics of Oxidation of Aluminum Nanoparticles.
Ying Li 1 Show Abstract
1 Collaboratory for Advanced Computing and Simulations, University of Southern California, Los Angeles, California, United States
Oxidation dynamics of single aluminum nanoparticles (ANPs) with three different sizes (26 nm, 36 nm and 46 nm) are studied using multimillion-atom reactive molecular dynamics simulations. Oxidation of the nanoparticle and the energy release rate are investigated for these ANPs comprised of different sizes of Al core coated with 3 nm thick amorphous aluminum oxide shell. The heat of the reaction comes from the thermite reactions between the aluminum and oxygen atoms. The onset temperature of core aluminum ejections is found to be independent of the core size, whereas the onset time of ejections and the time delay to the peak temperature increase rate depends on the size of the nanoparticle.
9:00 PM - Y9.16
Binder Free SnO2/CNT’s Nano-Composites as a Rechargeable Battery Anode.
D. Hernandez-Lugo 1 2 5 , F. Mendoza 3 5 , E. Febus 3 5 , D. Montano 4 5 , G. Morell 3 5 , B. Weiner 2 5 Show Abstract
1 NASA Harriet Jenkins Predoctoral Fellowship, Glenn Research Center, Cleveland, Ohio, United States, 2 Chemistry, University of Puerto Rico, San Juan United States, 5 Institute of Functional Nanomaterials (IFN), University of Puerto Rico, San Juan United States, 3 Physics, University of Puerto Rico, San Juan United States, 4 Mathematics, University of Puerto Rico, San Juan United States
Initial research on Li-based rechargeable battery materials was driven by the consumer electronics industry and continual research and design inventions are required to cope with the ever-demanding miniaturization and portability. Consumers are in constant demand for thinner, lighter, batteries with a larger autonomy. Commercial Li ion batteries mostly use graphite as the anode material because of its excellent stability. However, because the theoretical specific capacity of graphite is low (372 mAh g), sample opportunity exists for the development of new anode materials with higher capacities. The introduction of nanomaterials as electrodes in the cells, in place of conventional electrodes, was intended to provide higher lithiation capability and an overall better performance simply because of the nanomaterials extremely high surface area as compared to their bulk counterparts. Out of the many nanomaterials available, carbon nanotubes (CNTs) attracted much attention, mainly because of their excellent conductivity properties. Carbon nanotubes (CNTs) are predicted to reinforce novel composite materials because of their structural perfection, excellent mechanical properties and low density. Commercial batteries and most of the research efforts have used polymeric binders in the anodes, adding a redundant weight, ultimately reducing the specific capacity of the electrode. Advanced Li ion batteries, hence, need a binder-free electrode, to avoid such a type of capacity loss and which will include additional safety features. For this carbon nanotubes grown directly on a copper substrate need to be obtained. As part of this work SnO2/CNT’s grown on a copper substrate have demonstrated a capacity of 1000mAh/g for 10 cylcles with very little irreversible capacity. They have been grown by using Sulfur assisted Hot Filament Chemical Vapor Deposition. This new electrode will serve as an active material for lithium-ion battery anode and also as a matrix for other intercalation materials. Structural characterization such as X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Thermogravimetric analysis (TGA). Electrochemical Characterization consists of electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and charge discharge by using CR 2032 coin cells.
9:00 PM - Y9.17
Novel Porous Composite Material Containing Catalytic Nanoparticles for Hydrogen Production from Biofuel.
Nico Hotz 1 Show Abstract
1 Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States
In this study, a novel flow-based method is presented to place catalytic nanoparticles into a reactor by sol-gelation of a porous ceramic consisting of copper-based nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior. The goal of the herein presented method is to fabricate a foam-like porous ceramic containing a catalyst in form of nanoparticles in a direct one-step method by sol-gelation avoiding any separate coating or impregnation step. Previous studies have claimed that a one-step method is usually not possible due to the high sintering temperatures necessary for sufficient mechanical stability of the porous reactor material and that therefore ceramic foams typically have to be coated with the catalyst in a second step. The basic idea of this study is to use flow principles for the placement of catalysts in reactors. A sol-gelation method is applied to directly fabricate a catalytically active porous ceramic from a paste- or gel-like precursor, allowing for the direct precise placement of the catalytic ceramic in a reactor. This promises several advantages compared with the conventional method of coating or impregnating a rigid ceramic foam with a catalytic material in a second step after producing the inert ceramic foam in a first step.The catalytic activity of micro-reactors containing this foam-like ceramic is tested in terms of their ability to convert alcoholic biofuel (e.g. methanol) to a hydrogen-rich gas mixture with low concentrations of carbon monoxide (up to 75% hydrogen content and less than 0.2% CO, for the case of methanol). This gas mixture is subsequently used in a low-temperature fuel cell, converting the hydrogen directly to electricity. A low concentration of CO is crucial to avoid poisoning of the fuel cell catalyst. Since conventional Polymer Electrolyte Membrane (PEM) fuel cells require CO concentrations far below 100 ppm and since most methods to reduce the mole fraction of CO (such as Preferential Oxidation or PROX) have CO conversions of up to 99%, the alcohol fuel reformer has to achieve initial CO mole fractions significantly below 1%. The catalyst and the porous ceramic reactor of the present study can successfully fulfill this requirement.The results of the present study confirm that product gas mixtures with up to 75% hydrogen content and less than 0.2% CO content can be achieved, which is an excellent result. The reactor temperature can be kept as low as 220°C while obtaining a methanol conversion of up to 70%.
9:00 PM - Y9.18
Fabrication and Characterization of Thermoelectric CrSi2 Compound Induced by Mechanical Allloying.
Chung-Hyo Lee 1 , Young Kim 1 Show Abstract
1 Mat.Sci. & Eng., Mokpo National University, Muan Korea (the Republic of)
Mechanical alloying (MA) process is believed to be very effective in grain refinement and accumulation of crystal defects. In general, the so-called figure of merit (ZT) of thermoelectric material can be improved by grain refinement due to decreasing thermal conductivity. Materials with high ZT at elevated temperatures can be used for power generation application. Refractory metal silicides are potential candidates for power generation due to their superior physical and chemical properties at elevated temperatures. Particularly, CrSi2 compound is reported to be thermally stable in air up 1050 K.In the present work, thermoelectric CrSi 2 compound has been prepared by MA coupled with spark plasma sintering. An optimal MA and heat treatment conditions to obtain a single phase CrSi 2 with fine microstructure were investigated by the structural and thermal analysis of MA powders. Acknowledgements Following are results of a study on the "Human Resource Development Center for Economic Region Leading Industry" Project, supported by the Ministry of Education, Science & Technology(MEST) and the National Research Foundation of Korea(NRF).
9:00 PM - Y9.19
Reaction Mechanism of Organic Reactions on Nano-Porous Gold Catalysts.
Taketoshi Minato 1 2 , Eisuke Ito 2 , Yoshifumi Ishikawa 3 , Naoya Hatakeyama 3 , Masahiko Hara 4 , Yousoo Kim 2 , Naoki Asao 5 , Yoshinori Yamamoto 5 Show Abstract
1 Institute for International Advanced Interdisciplinary Research (IIAIR), International Advanced Research and Education Organization, Tohoku Univ., Sendai, Miyagi, Japan, 2 Advanced Science Institute, RIKEN, Wako, Saitama, Japan, 3 Department of Chemistry, Tohoku Univ., Sendai, Miyagi, Japan, 4 Interdisciplinary Grad. School Sci. Eng., Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 5 WPI-Advanced Institute for Materials Research, Tohoku Univ., Sendai, Miyagi, Japan
Recently, the catalytic activities of nano-porous (several tens nm) gold for gas phase reactions such as CO or methanol oxidations have been found by several groups. The activity of the nano-porous gold is characteristic and is not observed on other catalysts. For example, gold is a chemically stable metal in the bulk form, however, by the formation of nano-porous structure, gold show high catalytic activity for CO or methanol oxidation. Although the nano-particle (2-3 nm) of gold also show the catalytic activities, usually supporting materials (metal oxides or carbon materials) which modify the geometric/electronic structure of the gold is necessary to observe the catalytic activity. The nano-porous gold show the catalytic activity without supporting materials. Therefore, the elucidation of the reaction mechanism on nano-porous gold catalysts is important to develop new catalysts. We have found that the nano-porous gold show new catalytic activity for organic reactions in liquid phase such as silane or alcohol oxidation. However, the reaction mechanism is still unclear. To develop new catalysts, we have studied the reaction mechanism of the organic reaction by using surface science techniques (photo-electron spectroscopy and thermal desorption spectroscopy). Based on the observation of surface structure, electronic structure and adsorption structure, we will discuss the mechanism to produce the characteristic reactivity on nano-porous
9:00 PM - Y9.2
Reactive Metal Nanomaterials from Reduction of Borohydrides and Halides.
Andrew Purdy 1 , Albert Epshteyn 1 , Joel Miller 1 , Lisa Frank 1 Show Abstract
1 Chemistry Division, code 6123, Naval Research Laboratory, Washington, District of Columbia, United States
Ether containing solutions of the borohydrides of the light reactive metals (Li, Mg, Al, Zn) and group IVB metals (Ti, Zr, Hf) were reduced with either sodium-potassium alloy or Li powder, either alone or in combination. Reductions of soluble iodides and chlorides were also performed, and fluorinated additives were added to prepare carbon-coated core-shell particles. The salt by products were removed by solution in dimethylformamide, ethylenediamine or tetrahydrofuran for the lower melting metals, and by vacuum sublimation for the more refractory materials. General material characterization was done by powder x-ray diffraction, scanning electron microscopy, solid state NMR, and elemental analysis. Combustion energies were measured by TGA-DSC under an oxygen atmosphere after both short and long air exposure to determine air stability.
9:00 PM - Y9.21
Enhancement of Photocatalytic Reactivity of Fullerene/TiO2 by Electron Irradiation.
Jong Min Kum 1 , Sung Oh Cho 1 Show Abstract
1 Department of Nuclear and quantum engineering, KAIST, Daejeon Korea (the Republic of)
We irradiated electrons on fullerene coated TiO2 surface to enhance the photocatalytic reactivity. The electron beam irradiation can modify the molecular and bonding structures of target materials. It derives the change of characteristics such as absorbance, band position, and charge transfer. So, we tried to apply the properties of the electron beam irradiation technique into improvement of photocatalytic reactivity of semiconductor materials.Fullerene (C60) coated TiO2 nano-powder was used as a precursor material. C60 powder was dispersed in the chlorobenzene solvent mixed with TiO2 and stirred for 5hrs. The mixures of C60 and TiO2 was dried and washed by clean chlorobenzene solvent three times to remove impurities. To investigate the effect of electron irradiation, the precursor material composed with C60 and TiO2 was irradiated by electrons generated by thermionic electron gun. The powder samples are attached on the silicon wafer and loaded in vacuum of less than 2 × 10-5. Energy of electron was fixed at 50kV. Pt loading on the surface of both precursor and electron irradiated samples was followed by Pt deposition method using UV irradiation in H2PtCl6 solution. Hydrogen production to investigate the phtocatalytic reactivity was carried out using closed loop system. We used 500W Xe lamp as light source.Both carbon coating and electron irradiation enhanced hydrogen production rate of TiO2 photo catalyst. Moreover, as electron irradiation time increases, the hydrogen production rate also increases. Hydrogen production rate over C60/TiO2 irradiated by electron for 2 hrs was 3.913 mmol/hr, while 3.369 mmol/hr over precursor C60/TiO2.We observed red shift of the absorbance of C60/TiO2 after electron irradiation. The bandgap narrowing by electron irradiation can results in the enhancement of photocatalytic reactivity. If we characterize the difference of optical properties between the precursor and electron irradiated samples, the mechanism can be investigated. This technique also has potential to be applied in other photocatalyst materials.
9:00 PM - Y9.23
Synthesis of Molybdenum Disulfide Coaxial Nanotubes as Anode Material for Lithium Ion Battery Application.
Go-Woon Lee 1 2 , Janes Jelenc 3 , Soon Chang Lee 2 , Jung Min Kim 2 , Sang Moon Lee 2 , HoSeok Park 4 , Yun Suk Huh 2 , Maja Remskar 3 , Hae Jin Kim 1 2 Show Abstract
1 , Graduate School of Analytical Science and Technology, Daejeon Korea (the Republic of), 2 , Korea Basic Science Institute, Daejeon Korea (the Republic of), 3 , Josef Stefan Institute, Ljubljana Slovenia, 4 , Kyung Hee University, Gyeonggi-do Korea (the Republic of)
Here, we present a method for the facile synthesis of lithium-ion battery anode material based on MoS2 nanotubes. Molybdenum disulfide has a layered structure, resulting in the formation of two-dimensional layers by stacking together through weak van der Waals interactions. The weak interlayer interaction allows foreign ions or molecules to be introduced between the layers through intercalation. Thus, we developed a MoS2 nanotube material, showing the characteristic on the intercalation host to form a promising electrode material in high energy density batteries. MoS2 coaxial nanotubes were produced by sulfurizing Mo6S2I8 nanowires which was synthesized by chemical direct reaction. The products are characterized by X-ray diffraction, transmission electron microscopy and N2 adsorption analysis techniques. The results show that the MoS2 have high reversible capacities (715mAh/g). In addition, we present experimental results showing how a hybrid structure comprising of carbon nanomaterials in a MoS2 nanotubes can be used to enhance conductivity in energy storage applications. With this hybrid technique we demonstrate the high-power lithium ion batteries to the success of electric, hybrid electric vehicles and next generation electronic devices.
9:00 PM - Y9.24
Charge-Discharge Property of LiFePO4 in the Middle-Temperature Region below 150°C.
Tomochika Kurita 1 2 , Makoto Yaegashi 2 , Shin-ichi Nishimura 2 , Tsutomu Tanaka 1 , Takuya Uzumaki 1 , Atsuo Yamada 2 Show Abstract
1 , Fujitsu Laboratories, Ltd., Atsugi-shi, Kanagawa, Japan, 2 Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
Large-scale lithium-ion batteries operating at middle-temperature region may provide additional advantageous aspects such as higher power and application of new materials which are inactive at ambient temperature. Here we apply LiFePO4 cathode to middle-temperature region and its charge-discharge properties were tested. By selecting suitable electrolyte and battery components, stable operation was attained for no less than 20 cycles below 120°C. High-rate performance was improved as operating temperature increased up to ~80°C, but suffered from abrupt increase in polarization above ~80°C, where we found some signals of side reactions. Change in phase diagram and its size dependency were not confirmed at T < 120°C and r > 40 nm.
9:00 PM - Y9.26
Minimization of Lattice Thermal Conductivity of Higher Manganese Silicide: A Microstructural Approach.
Suresh Perumal 1 , Ujwala Ail 2 , Stephane Gorsse 2 , Arun Umarji 1 Show Abstract
1 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India, 2 Institut de Chimie de la Matière Condensée de Bordeaux , ICMCB-CNRA, Bordeaux France
Thermoelectirc materials can also be solutions to the renewable energy sources by directly converting heat into electricity and vice versa. In this context, Transition Metal Silicides can be good candidate for high temperature thermoelectric applications due their semiconducting nature, structural and thermal stabilities at elevated temperature ranges . Higher Manganese Silicides (HMS) show semiconducting nature with range of band gap from 0.4 to 0.77eV, depending upon their stoichiometry and tetragonal crystal structure with space group of P-4n2 (Nowotny chimney-ladder) . HMS is a promising material for thermoelectric applications due to its high seebeck coefficient and electrical conductivity of (120 μV/K and 5.4 x 104 S/m at 300K). The contribution of lattice thermal conductivity to total thermal conductivity is about 2.4 W/m.K compared to electronic contribution (0.3 W/m.K) . Hence, further reduction in the lattice thermal conductivity possibly by engineering the microstructure can be useful in enhancing the figure of merit . In this regard, an attempt has been made for reducing the lattice thermal conductivity by engineering on microstructure of secondary phase of Si in the matrix of MnSi1.727. The ingots of HMS (Eutectic composition 66.4 at% of Si) have been synthesized by vacuum arc melting from high purity elements of Mn and Si under Argon atmosphere. The arc melted ingots are crushed into fine powder for powder X-ray diffraction studies which confirmed the MnSi1.727 phase with secondary phase of Si. The fine powders of HMS are hot-pressed (42MPa) using graphite die under argon atmosphere at 1333K for 5 minutes. These pellets are subjected to heat treatment in the different temperatures followed by quenching, whereby microstructures can be changed according to heat treatment condition. Change in the temperature leads to different microstructures of secondary phase of Si and act as phonon scattering centre whereby total thermal conductivity can be reduced and possible for enhancing figure of merit. In this work, the electrical resistivity, seebeck coefficient, lattice and total thermal conductivity as function of temperature will be discussed. The effect of microstructure change on powder factor and figure of merit as function of temperature will be presented.
9:00 PM - Y9.27
Enhanced Electromechanical Responses of P(VDF-CTFE)/PMMA Actuators.
Yang Liu 1 , Ran Zhao 1 , Junhong Lin 2 , Gokhan Hatipoglu 1 , Minren Lin 2 , Qiming Zhang 1 2 Show Abstract
1 Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Ionic electroactive polymer (i-EAP) actuators are of great interest because of the large strain generated under low voltage (<5 volts). On the other hand, one critical issue in applying the i-EAPs for these applications is how to significantly improve the electromechanical performance, including actuation strain, blocking force and efficiency. Here, we present our recent progress in addressing these issues by cross-linking P(VDF-CTFE) and PMMA mixture materials for i-EAP actuators. Compared to the conventional polymers, such as Nafion and Aquivion that are popularly used in i-EAP actuator study, we developed P(VDF-CTFE)/PMMA actuators with remarkably enhanced strain and significantly depressed charge consumption. The experimental results show that the bending curvature of an ~8mm long actuator under 4V DC bias reaches 0.8mm-1 , which is the largest value that has ever been obtained from an i-EAP membrane actuator. The charge accumulated in actuating this transducer 0.0015C/mm2 is also much smaller than actuators made with other ionomers. This indicates a larger electromechanical efficiency from P(VDF-CTFE)/PMMA actuators since all of them have similar elastic modulus values. Furthermore, an enhanced blocking force 50mN is also observed from the 2mm*15mm P(VDF-CTFE)/PMMA actuator, which is again due to the better electromechanical coupling between the ions and the polymer matrix. In conclusion, P(VDF-CTFE)/PMMA is a promissing actuator material with largely enhanced strain, force and efficiency.
9:00 PM - Y9.3
Synthesis and Characterization of a New Energetic Plasticizer: Bis(2,2-dinitropropyl Ethylene) Formal.
Yun Chen 1 , Mingyang Ma 1 , Jin Seuk Kim 2 , Younghwan Kwon 1 Show Abstract
1 Chemical Engineering, Daegu University, Gyeongsan, Gyeongbuk, Korea (the Republic of), 2 , ADD, Daejeon Korea (the Republic of)
Plasticizers are additives widely used in the polymer industry. For specific applications in the field of high energy materials, energetic functional groups such as azido, nitro and difluoramine groups have been introduced in the plasticizers, known as energetic plasticizers. Incorporation of these explosophores increases the internal energy of the formulation, in addition to improving the overall oxygen balance. Several energetic plasticizers, such as nitratoethyl nitramine (NENA), butanetriol trinitrinitrate (BTTN), trimethylolethane trinitrate (TMETN), bis(2,2-dinitropropyl) acetal/bis(2,2-dinitropropyl)formal (BDNPA/F), 2,4-/2,6-dinitroethylbenzene/2,4,6-trinitroethylbenzene, and GAP oligomer, have been developed worldwide for use in the field of high energy materials. The optimum energetic plasticizers are required to have low glass transition temperature, a low viscosity, a low ability to migrate and a high oxygen balance. It should also be thermally stable and have low impact sensitivity. These demands are in many cases contradictory and it is thus not easy to find the ultimate energetic plasticizer. In this study, a new energetic plasticizer, bis(2,2-dinitropropyl ethylene) formal (BDNPEF), has been synthesized by using the aldol condensation reaction of 2,2-dinitropropanediol, ethylene glycol, and formaldehyde catalyzed with Lewis acid. Bis(2,2-dinitropropyl) formal (BDNPF) is also obtained as a side product. Structural integrity of the synthesized energetic plasticizer is identified by using elemental analyzer, GC-Mass, 1H and 13C NMR. Thermal properties of the plasticizer are measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). BDNPEF exhibits -66.5 oC of glass transition temperature and 253 oC of thermal decomposition temperature from DSC measurement. Plasticizing effect of BDNPEF on uncured GAP prepolymer is studied and compared to other energetic plasticizers. The viscosity of uncured GAP prepolymer at 60 o is decreased from 0.966 to 0.244 Pas by adding 50% of BDNPEF. BDNPEF is also found to be effective in lowering the glass transition temperature of GAP prepolymer.
9:00 PM - Y9.4
Synthesis and Characterization of a Reactive Energetic Plasticizer with Clickable Functionality in Polyurethane Binders.
Yan Xu 1 , Ho-Joong Kim 1 , Jin Seuk Kim 2 , Younghwan Kwon 1 Show Abstract
1 Chemical Engineering, Daegu University, Gyeongsan, Gyeongbuk, Korea (the Republic of), 2 , ADD, Daejeon Korea (the Republic of)
Plasticizers are additives widely used in the polymer industry. Generally, they are known to improve processability by lowering the viscosity during the formulation as well as impart low temperature flexibility by lowering the glass transition temperature of the polymers. For specific applications in the field of high energy materials, energetic functional groups such as azido, nitro and difluoramine groups have been introduced in the plasticizers, known as energetic plasticizers. Incorporation of these explosophores increases the internal energy of the formulation, in addition to improving the overall oxygen balance. Since plasticizers, either inert or energetic, used in these applications are externally incorporated with the polymers, they are inherently hampered by the migration of plasticizers out of the polymer matrix, resulting in long-term deterioration of properties such as impact sensitivity, storage stability, and mechanical properties, etc. Therefore, it has been one of major issues, especially in the field of high energy materials, to provide energetic plasticizers with new concepts. Hence, this research focuses on the design, synthesis and characterization of a reactive energetic plasticizer and its application to polyurethane binders. Three main concepts for designing the structure of the reactive energetic plasticizer are described. Firstly, the plasticizer is designed to have all the structural requirements as general plasticizers, for instance, the range of molecular weights and structurally ether backbone for miscibility with polyether prepolymers. Secondly, the energetic C-nitro groups are incorporated in the structure, due to higher thermal stability than O-nitro groups. Lastly, the plasticizer is designed to prevent inherent migration from the polymer matrix. This can be realized by introducing "clickable" reactive functional groups in the plasticizer. The reactive energetic plasticizer is synthesized by using the aldol condensation reaction of alcohol compounds and formaldehyde catalyzed with Lewis acid. Structural integrity of the synthesized reactive energetic plasticizer is identified by using elemental analyzer, GC-Mass, 1H and 13C NMR. Thermal properties of the plasticizer are measured by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).The reactive energetic plasticizer can work properly as a general plasticizer in the beginning of the formulation process and then can be incorporated in curing process of PU binders through the click reaction, preferably, of alkyne groups in the plasticizer and azide groups in the prepolymer.
9:00 PM - Y9.5
Direct-Write Assembly of Micro-Energetic Materials.
David Kolesky 1 , Eric Duoss 2 , Kyle Sullivan 2 , Cheng Zhu 2 , Joshua Kuntz 2 , Doug Tanaka 1 , Christopher Spadaccini 2 , Jennifer Lewis 1 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States
Energetic materials are biphasic systems composed of an oxidizing and metal fuel species. These materials are capable of releasing large amounts of stored chemical energy upon ignition. Energetic materials are commonly used as propellants, pyrotechnics, and explosives, but novel applications such as energy sources for microelectromechanical systems (MEMs) are beginning to emerge. However, a fundamental understanding of how microstructure influences the performance, sensitivity, and stability of energetic materials must be developed in order to optimize current systems and enable novel applications. We are creating micro-energetic materials with tailored architectures via direct ink writing (DIW) of highly ordered oxide structures that are in-filled with a metal fuel using electrophoretic deposition. Ultimately, we aim to establish the relationship between their microstructure and key performance properties, including propagation velocity and energy density. This research represents an initial step towards integrating materials discovery, design, and fabrication of micro-energetic materials, which may be readily extended to other multiphase functional materials.
9:00 PM - Y9.6
First Principles Studies of Oxygen Transfer at Buried Metal/Metal Oxide Interfaces: Implications for the Performance of Energetic Nanolaminates
Carissa Goldstein 1 , Edward Mily 1 , Jon-Paul Maria 1 , Donald Brenner 1 , Douglas Irving 1 Show Abstract
1 Materials Science and Engineering, N.C. State University, Raleigh, North Carolina, United States
Materials composed of metal/metal-oxide layers with nanometer-scale thicknesses are a new class of energetic structure with the potential for controllable sensitivity and power output that in principle can deliver energy densities up to four times larger than conventional explosives such as RDX. We present results from our first principles calculations that are used to investigate the initial stages of oxygen transport across the metal/metal-oxide interfaces in select reactive nanolaminate structures. The original interfaces explored were based on our companion experimental effort that uses Al and Ti with Cu2O. Experimentally, nanolaminates with Al are found to have a lower power output relative to those made with Ti. These results qualitatively agree with our transition state calculations that show a higher chemical barrier for oxygen transport across the Al/Cu2O interface compared to transport of oxygen across the Ti/Cu2O interface. Other systems were chosen based on the lattice mismatch, structural similarity, and the degree of exothermicity associated with oxygen transfer, such as Zr with ZnO. The results presented are providing important data related to oxygen exchange mechanisms and their relationship to structure and bond strengths, and give new insights into how to control sensitivity and power output through material selection. This project has been supported by the Army Research Office through grant # W911NF-10-1-0069.
9:00 PM - Y9.7
Synthesis and Coating of Aluminum NanoCrystals.
Dan Kaplowitz 1 , Michael Zachariah 1 Show Abstract
1 , University of Maryland, College Park, Maryland, United States
We show a low temperature gas-phase synthesis route to produce faceted aluminum crystals in the aerosol phase. Use of triisobutylaluminum whose decomposition temperature is below the melting point of elemental aluminum enabled us to grow nanocrystals from its vapor. TEM shows both polyhedral crystalline and spherical particle morphologies, but with the addition of an annealing furnace one can significantly enhance production of just the polyhedral particles. The results on surface passivation with oxygen suggest that these nanocrystals are less pyrophoric than the corresponding spherical aluminum nanoparticles, and combustion tests show an increase in energy release compared to commercial nanoaluminum.Further studies have involved using an in-situ coating method to create a Ni barrier layer for which we have evaluated combustion performance.
9:00 PM - Y9.8
Encapsulation of Perchlorate Salts within Metal Oxides for Application as Nano-Energetic Oxidizers.
ChunWei Wu 1 , Kyle Sullivan 1 , S. Chowdhury 1 , Guoqiang Jian 1 , Michael Zachariah 1 Show Abstract
1 , University of Maryland, College Park, Maryland, United States
In this work, high oxygen content strong oxidizer perchlorate salts were successfully incorporated into current nano-thermite composite formulations. The perchlorates were encapsulated within mild oxidizer particles through a series of thermal decomposition, melting, phase segregation and re-crystallization process occurred within confined aerosol droplets. This approach enables the use of hygroscopic materials by stabilizing them within a matrix. Several samples including Fe2O3/KClO4, CuO/KClO4 and Fe2O3/NH4ClO4 composite oxidizer particles have been created. The results show that these composite systems significantly outperform the single metal oxide system in both pressurization rate and peak pressure. The ignition temperatures for these mixtures are significantly lower as compared to the metal oxide alone, and time resolved mass spectrometry shows O2 release from the oxidizer also occurs at a lower temperature and with high flux. The results are consistent with O2 release as the controlling factor in determining the ignition temperature. High speed imaging clearly shows a much more violent reaction. The results suggest that a strategy of encapsulating a very strong oxidizer, which may not be environmentally compatible, within a more stable weak oxidizer offers the opportunity to both tune reactivity and to employ materials that previously would be prohibited.
9:00 PM - Y9.9
Synthesis and Reactivity of Nano-Ag2O as an Oxidizer for High Yield Antimicrobial Energetic Systems.
Kyle Sullivan 1 , Nick Pickiel 1 , Michael Zachariah 1 Show Abstract
1 , University of Maryland, College Park, Maryland, United States
This work investigated Ag2O as a potential oxidizer in antimicrobial energetic systems. Ultrafine Ag2O was synthesized, and its performance in nanoaluminum-based thermite systems was evaluated using a constant volume combustion cell. The Ag2O alone was found to be a relatively poor oxidizer, but it performed well when blended with more reactive oxidizers, CuO and AgIO3. Time resolved mass spectrometry was used to investigate the reaction mechanism in more detail. Post-reaction analysis confirmed the production of Ag, but it was seen to exist in a matrix with Cu in the Al/CuO/Ag2O ternary system. The product in surface contact with Al2O3 suggested a reactive sintering mechanism occurred. The results indicate that Ag2O, while a poor oxidizer itself, can be integrated into more reactive systems to produce high yields of biocidal silver. The morphology of the final product, however, indicates that a large amount of the silver may not be surface-exposed, a result which would negatively impact the biocidal activity.
M. Riad Manaa Lawrence Livermore National Laboratory
Choong-Shik Yoo Washington State University
Evan J. Reed Stanford University
Michael S. Strano Massachusetts Institute of Technology
Y10: Thermal and Shock Processes
Wednesday AM, November 30, 2011
Room 309 (Hynes)
9:30 AM - Y10.1
Phase Transformations in Semiconductor Nanocrystals under Intense Ultraviolet Excitation and Shockwave Compression.
Joshua Wittenberg 1 2 , Timothy Miller 1 , Maxwell Merkle 2 , Paul Alivisatos 2 , Aaron Lindenberg 1 Show Abstract
1 , Stanford University, Oakland, California, United States, 2 , University of California, Berkeley, California, United States
Structural phase changes play an important role in processes ranging from polymorphic transformations during geological events to the production and tempering of steel. They have also garnered recent interest due to the applicability of phase change materials to nonvolatile storage media. Semiconductor nanocrystals, owing to their small size, transform as single crystalline domains, and the transformation of an individual crystallite is complete within approximately ~10ps, based on recent simulations. As a result, nanocrystals are promising model systems through which to study polymorphic phase transformations as well as potential candidates for rapidly switching data storage bits. The behavior of CdSe nanocrystals shocked to stresses of 2–3.75GPa has been studied. Above 3GPa a near-complete disappearance of the first excitonic visible absorption feature and broadening of the low-energy absorption edge were observed, consistent with a wurtzite to rocksalt structural transformation. The transformation pressure was reduced relative to hydrostatic compression in a diamond anvil cell, and the rate increased, attributed to shock induced shear stress along the reaction coordinate. The especially rapid rate observed for a 3.75GPa shock suggests multiple nucleation events per particle. At laser fluences on the order of 100mJ/cm2, melting of rod-shaped CdSe nanocrystals has been observed due to rapid thermalization of the large number of electron-hole pairs generated by photoexcitation. CdSe nanocrystals possess a wurtzite crystal structure, and therefore have a non-centrosymmetric unit cell. We will report experiments which measure the timescale of the melting transformation, using incoherent second harmonic scattering to probe the increase in structural centrosymmetry upon melting. The transformation dynamics have also been studied at the Advanced Photon Source at Argonne National Laboratory, using X-rays to probe the loss of crystalline order following photoexcitation by an intense laser pulse.
9:45 AM - Y10.2
Influence of Environmental Gas on Reaction Behavior and Phase Formation in Ti/2B Reactive Multilayer Foils.
Robert Reeves 1 , Alexander Tappan 1 , Joel McDonald 1 , Eric Jones, Jr. 1 , David Adams 1 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
The Ti/2B reactive system has been studied by both the combustion synthesis and energetic materials communities for its attractive properties, namely its ability to form the TiB2 ceramic compound and for its high energy release through a virtually gasless reaction. Previous work on other systems has indicated that the environmental gas can have a significant effect on both the reaction behavior and the resulting reaction products. We report on the effects of varying environmental gas properties on the reaction behavior and product formation for sputter-deposited Ti/2B reactive multilayers. The reaction environment was varied from atmospheric conditions to vacuum. An inert ambient gas (He) was also utilized to study the influence of a nonreactive, thermally absorptive environment. First, samples were reacted in the propagating reaction mode and the average reaction wave velocities were determined for the different environmental conditions through high speed imaging. Propagation speeds for 1.6 micron thick multilayers were in the range of 10-40 m/s depending on bilayer thickness (i.e., reactant layer perioidicity). Samples were also ignited in the thermal explosion mode and the effect of the atmosphere on the self-ignition behavior is discussed. Differential scanning calorimetry was performed in both oxidizing and inert environments to determine the overall contribution of any reduction/oxidation reactions to the system’s exothermicity and the importance of this additional heat release is considered. The product phase composition was verified through x-ray diffraction analysis and the role of the environmental gas is discussed. The extent of oxygen penetration into the multilayer stack was also investigated through depth-profiling Auger electron spectroscopy.This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.
10:00 AM - Y10.3
Non-Equilibrium Molecular Dynamics Studies of Interfacial Chemistry in Shocked Ni/Al Nanolaminates.
Jason Quenneville 1 , Timothy Germann 2 , Naresh Thadhani 3 Show Abstract
1 , Spectral Sciences, Inc., Burlington, Massachusetts, United States, 2 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
The response of Ni/Al composite materials to shock loading has been studied using non-equilibrium molecular dynamics and an EAM force field. The main thrust of our research is to gain a better understanding of the chemistry that occurs at the Ni/Al interface when the real material is shocked. The simulation cells consist of layered Ni and Al laminates with at least 3 million particles in a 1:1 mole ratio. Initial geometries were chosen so as to identify the factors important to reaction in the complex macro-scale material. Specifically, we vary the orientation of the interface with respect to the shock wave and the geometry of the interface (i.e., deviation from planarity) to study how mixing and reactivity of Ni and Al are affected. Preliminary results show that peak pressure is greater when the shock direction is parallel to the Ni/Al interface plane, in agreement with results from continuum-scale simulations. Comparison of our computational results with experimental observations is an important part of this collaborative effort and is discussed in the paper.
10:15 AM - Y10.4
Exothermic Reaction Characteristics of Ball Milled and Ultrasonic Consolidated Al/Ni Powder Compacts.
Claus Rebholz 1 2 , Anastasia Hadjiafxenti 1 2 , Ibrahim Gunduz 1 2 , Panos Epaminonda 1 , Dinc Erdeniz 2 , Theodora Kyratsi 1 , Teiichi Ando 2 , Charalabos Doumanidis 1 Show Abstract
1 Mechanical and Manufacturing Engineering, University of Cyprus, Nicosia Cyprus, 2 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Nanoscale materials that exhibit self-propagating exothermic reactions (SPER) are promising energy sources for thermal manufacturing, owing to their ability to provide intense localized heat. These materials are mainly manufactured in the form of bimetallic multilayer foils using magnetron sputtering. Alternative processing routes include (1) mechanical alloying in the form of ball milling (BM), in which powder mixtures are subjected to repeated plastic deformation in order to generate lamellar structures within the powders and imitate sputtered multilayers; and (2) ultrasonic powder consolidation (UPC) as a way of improving the metallurgical bonding between the two reagents during consolidation by exploiting ultrasonic energy that facilitate interparticle mixing and diffusion. In this presentation we focus on SPER in consolidated pellets of ball milled aluminum (Al) and nickel (Ni) powders at a composition corresponding to AlNi3, but also report first results on compacts with the same composition produced by UPC. The reaction characteristics of the ball milled samples observed using high speed optical and infrared imaging revealed that the thermal wave velocity, maximum reaction temperature and ignition initiation duration decreased with increasing milling times after 1 hour. The formation of a bi-modal structure with nanoscale lamella of Al and Ni surrounding thicker Ni layers and a reduction in overall powder size at longer milling hours was observed. X-Ray Diffraction (XRD) analysis after ignition tests showed that the AlNi3 amount increased with increasing milling time. Thermal analysis using interrupted Differential Scanning Calorimetry (DSC) in combination with XRD revealed that the ball milled pellets have similar characteristics to nanoscale magnetron sputtered multilayer foils in terms of phase formation sequence and exothermic peak shifts. First results on consolidated Al and Ni powders produced by UPC under different processing conditions indicate that oxide and pore free compacts can be formed, exhibiting SPER after reaching the aluminum melting temperature. We believe that BM and UPC are novel and economical processing routes for generating powders that can be shaped into useful geometries (such as rolled into thin sheets) for thermal manufacturing applications.
10:30 AM - Y10.5
Air-Stable Reactive Metal Nanopowders from In Situ Sonochemical Decomposition of Group 4 Tetrahydroaluminates and Borohydrides.
Albert Epshteyn 1 , Andrew Purdy 1 , Peter Johnsen 2 , Joel Miller 1 Show Abstract
1 , Naval Research Laboratory/SSD, Washington, District of Columbia, United States, 2 NRL/SEAP , US Naval Research Laboratory, Washington, District of Columbia, United States
Air-stable reactive metal nanopowders were prepared via an in situ reaction of the respective group 4 transition metal (Ti, Zr, or Hf) chloride with lithium aluminum hydride and/or lithium borohydride producing the respective group 4 borohydride and/or tetrahydroaluminate complex, which subsequently decomposes releasing H2 gas, and forming a black powder. The as-prepared materials are amorphous, and contain LiCl byproducts. Following ether solvent removal, the materials were annealed under vacuum to temperatures between 600°C and 1100°C, and monitored by XRD at temperature intervals, which showed the crystallization of various phases and the sublimation of the LiCl byproduct. The materials were then characterized for their air-stability and this was correlated to their morphology and elemental content. The morphology of the powders was observed via SEM and HRTEM showing agglomerated structures from 10s to 1000s of nanometers in diameter, comprizing 2 nm to 10 nm crystalline grains. EDS and traditional elemental analysis were carried out on all samples to determine elemental makeup, confirming the presence of both the group 4 metal and aluminum and boron, where expected. Thermo-chemical data were obtained for the reaction of the powders with O2 via TGA/DSC showing significant energy release – with all samples producing a majority of the theoretical energy expected from the elements. The materials were then characterized by SS-MAS-NMR to correlate the morphological and thermo-chemical data with the NMR data.
Y11: Energetic Formulations and Applications
Wednesday PM, November 30, 2011
Room 309 (Hynes)
11:15 AM - Y11.1
Electrophoretic Deposition of Binary Energetic Thermites.
Kyle Sullivan 1 , Marcus Worsley 1 , Joshua Kuntz 1 , Alex Gash 1 Show Abstract
1 , Lawrence Livermore National Laboratory, Livermore, California, United States
This work investigates the use of electrophoretic deposition (EPD) as a means to prepare thin films of well-mixed Al / CuO particulate composites. EPD films were compared to those that have been drop cast, where a premixed thermite suspension was dropped directly onto a substrate with a pipette and allowed to dry. Films were examined using electron microscopy, and the combustion characteristics were analyzed with high-speed videos. The results show that films prepared by EPD show much more homogeneous mixing of the constituents, leading to a large enhancement in the performance and control of the energy release. Thermite films were also deposited onto patterned electrodes, with very fine feature sizes, which can subsequently be heated with a tunable current pulse. Patterned electrodes are being used for mechanistic investigations of the ignition and combustion, but are also particularly useful for characterizing and developing thermites for micro-energetic applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Tracking #LLNL-ABS-488552
11:30 AM - Y11.2
Boride-Based Materials for Energetic Applications.
Michael Whittaker 1 , Jesse Sabatini 3 , Paul Anderson 3 , Raymond Cutler 2 Show Abstract
1 Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States, 3 , US Army RDECOM-ARDEC, Picatinny Arsenal, New Jersey, United States, 2 , Ceramatec Inc., Salt Lake City, Utah, United States
Boron has long been recognized as fuel for rocket propulsion and other energetic applications where high energy density is required. The oxidation of boron to boron oxide (B2O3) is highly exothermic on both a volume and mass basis. The main problems with using boron have been obtaining complete combustion and the high cost of the material. Metal borides (AlB2, MgB2, Mg0.5Al0.5B2, SiB6, AlB12, and MgAlB14), boron carbide (B4C), and boron phosphide (BP) were compared to B, Mg, Al, and AlMg as potential fuels. Surface area, particle size, and SEM imaging were used to characterize the powders. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to characterize the response of these powders to oxidation in flowing air. Through these techniques it was confirmed that adding magnesium or aluminum to boron increased the oxidation efficiency of boron by forming metal-borate crystals (9B2O3.2Al2O3 and 3B2O3.MgO, respectively) which removed liquid B2O3 from the surface of oxidizing particles and allowed for increased combustion efficiency. Aluminum also greatly increased the oxidation efficiency of B4C by a similar mechanism. Silicon did not improve the oxidation rate of boron and may further retard the oxidation process through the formation of glassy silicon borates. Simple powder mixtures were not significantly less sensitive than the aluminum standard, but the formation of boron-based compounds (borides, carbides, or phosphides) increased the insensitivity of the materials. However, AlB12, AlB3C, AlMgB14 and SiB6 did not react completely or quickly, suggesting that they may be poor energetic materials. AlB2, MgB2 and Al0.5Mg0.5B2 were the only materials that oxidized to greater than 85% of their theoretical values while exhibiting increased insensitivity, making them top candidates for further energetic testing. Selected materials were tested in pyrotechnic or explosive formulations and their performance is discussed relative to the characterization data.
11:45 AM - Y11.3
Galvanic Etching to Realize on-Chip Nanoporous Silicon Energetic Composites.
Collin Becker 1 , Luke Currano 1 , Wayne Churaman 1 , Christopher Morris 1 , Conrad Stoldt 2 Show Abstract
1 , U.S. Army Research Laboratory, Adelphi, Maryland, United States, 2 Mechanical Engineering, University of Colorado, Boulder, Colorado, United States
Silicon (Si) is a readily oxidizable material that can function as the fuel for an energetic material. Large surface area, nanoscale Si materials have recently been used in impressive energetic compositions. In this work, nanoporous silicon (nPS) is formed on Si substrates by a galvanic etching method in hydrofluoric acid (HF) based electrolytes. In the electrolyte, Si etching occurs as an internal current arises from the electrochemical potential between Si and a thin film of platinum (Pt) sputtered directly on the Si. Processing parameters including electrolyte composition, wafer dopant concentration, and etch time control the porosity, surface area, and pore size. Relative to conventional electrochemical etching, galvanic etching is more compatible with microsystems fabrication and allows greater flexibility in design of on-chip energetic devices. Samples with specific surface area near 800 m2/g, pores similar to 3 nm, and thicknesses greater than 100µm are fabricated. Energetic composites are produced by filling the pores with strong oxidizers, and the hydrogen termination of nPS renders the material resistant to slow oxidation as confirmed by Fourier transform infrared spectroscopy (FTIR). In on-chip burn rate tests using sodium perchlorate (NaClO4) as the oxidizer, a flame front traveling > 3 km/s is observed. Additionally, a comprehensive differential scanning calorimetry (DSC) analysis of nPS oxidation in air, nitrogen, and with NaClO4 reveals that the highly exothermic reaction is triggered as low as 133°C, well below Si backbond oxidation, hydrogen desorption, or NaClO4 melting. Reaction products collected from bomb calorimetry under a nitrogen atmosphere are confirmed with Raman spectroscopy and TEM to include nanoscale spherical amorphous silica particles indicating a very hot reaction. Lastly, using only a high pressure oxygen atmosphere (~420 psig), nPS can be ignited to yield similar nanoscale silica particles as with NaClO4.
12:00 PM - Y11.4
Nitrocellulose and BKNO3 Based Igniters for Gun Systems.
Eugene Rozumov 1 , Thelma Manning 1 , Joseph Laquidara 1 , Kimberly Chung 1 , Duncan Park 1 , Viral Panchal 1 Show Abstract
1 , Armament Research Development Engineering Center, Picatinny, New Jersey, United States
Common igniters such as black powder, benite, and boron potassium nitrate BKNO3 are routinely employed in all calibers of gun systems. Armament Research Development Engineering Center (ARDEC) has pursued efforts to improve the ignition of gun propellants which has been demonstrated to be the root cause of many tribulations for gun systems. We have developed several extrudable nitrocellulose-BKNO3 based igniter materials that are more energetic, exhibit smaller ignition delay times, and are less sensitive than most traditional igniters. We have demonstrated this via subscale testing, and static firing. High speed video during static testing has demonstrated significantly more consistent, intense, and rapid flame generation in comparison to Benite leading to improved ignition effectiveness of the propellant bed.
12:15 PM - Y11.5
Reinforcement of Triazole-Cured Binders with Carbon Nanotubes.
Joshua Carter 1 , Anna Merritt 1 , Brandon Ferguson 1 , Tara Cross 1 Show Abstract
1 Synthesis and Formulations, NAWCWD, China Lake, California, United States
This study documents the mechanical reinforcement offered by dispersed carbon nanotubes (CNTs) in a triazole-cured binder system. Triazole-cured binders are made through the 1,3-dipolar cycloaddition of azides and acetylene. They feature a robust cure mechanism that has been shown to be impervious to moisture, a benefit that has led to their investigation as an alternative to the hydroxyl-terminated polybutadiene binders that are utilized in state-of-the-art rocket propellants and explosives. The moisture-insensitivity of triazole-cured binders, however, is offset by their relatively low stress capacity. The addition of CNTs has been shown to improve the strength of many composite systems when efficient load transfer from the binder to the ultra strong nanotubes can be achieved, making triazole-cured binders an excellent candidate for reinforcement.This work describes the preparation of triazole-cured binder/CNT composites prepared through ultrasonic mixing of the CNTs into a plasticizer prior to their addition into a mixture of azido prepolymer and trifunctional acetylenic curative species. Multiple plasticizers are examined for their ability to maintain stable dispersions of both multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs), and multiple CNT concentrations are tested for dispersion stability and enhancement of the mechanical properties in the composite.Microscopy of the cured products is used for quick evaluation of both good and poor quality dispersions while thermal conductivity measurements are used to demonstrate potential effects of carbon nanotubes on burning rates. Mechanical properties characterization show the maximum tensile strength is achieved with stable dispersions. Exceeding the stable dispersion limit with higher loadings of CNTs results in poorly-dispersed CNT aggregates and a negative effect on the tensile strength of the the composite.
12:30 PM - Y11.6
Self-Sustained Oxidation of Al/Zr Multilayers.
Howie Joress 1 , Sara Barron 1 , Natan Aronhime 1 , Kenneth J. Livi 2 , Timothy Weihs 1 Show Abstract
1 Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 HRAEM Facility of the Integrated Imaging Center, Johns Hopkins University, Baltimore, Maryland, United States
Intermetallic formation reactions are known to self-propagate in multilayer foils with a rapid release of heat, but cooling rates are typically very fast for foils thinner than 100 μm. Some energetic applications require a longer “burn time” with the duration at high temperatures as long as several seconds. Here we report that in Al/Zr multilayered foils, a rapid intermetallic reaction can ignite a slower self-sustaining oxidation reaction with the foils remaining above 1200 K for more than 2 s. This is in contrast to foils reacted in vacuum that reach temperatures above 1200 K due to the intermetallic reaction but cool to room temperature in less than .5 s in the absence of oxygen. It is also in contrast to multilayer foils of other chemistries, such as Al/Ni or Al-rich Al3/Zr, in which the oxidation is not sufficiently rapid to enable a self-sustaining oxidation in thin foils. After reactions in the Al/Zr foils, the Zr-rich oxide surface layers are thicker than 5 μm, and their growth results in a Zr depletion layer surrounding the foil’s intermetallic core. Here we present time-temperature data for reactions in air and vacuum and post-reaction characterizations of the reaction products.
12:45 PM - Y11.7
Investigating and Comparing the Thermal Behavior of Three Types of Polyethylene/Paraffin Blends for Form-Stable Phase Change Materials.
Fang Chen 1 , Michael Wolcott 1 Show Abstract
1 , WSU, Pullman, Washington, United States
Thermal properties of form-stable phase change material (PCM) are of great importance because of their effect on material’s energy saving ability and application. Paraffin wax with eighteen carbons on the backbone was compounded with HDPE, LDPE and LLDPE separately utilizing a parallel co-rotating twin screw extruder. Thermal behaviors of these partially miscible blends were investigated by differential scanning calorimeter (DSC), thermal conductivity meter, thermo gravimetric analysis (TGA), and leakage test. The thermal transition temperatures and thermal enthalpy of each component were collected to delineate interaction between paraffin and PE based on blend composition. Thermal stability and thermal conductivity of PE/Paraffin blends were also inspected. Experimental and theoretical thermal conductivity results were compared. The results indicated that the glass transition temperature of paraffin and PE were close and did not change much in their blends. Melting temperature and crystallization temperature of paraffin and PE dropped with increasing amount of the other component. Enthalpy of HDPE in its blends with paraffin remained stable to some degree while enthalpy of LDPE and LLDPE dropped with increasing of paraffin content. Enthalpy of paraffin in PE also dropped with increasing of PE content. Two degradation steps were observed for all the PE/Paraffin blends. Thermal stability of paraffin in PE was ranked in an order of LLDPE>LDPE>HDPE. Better thermal stability was investigated for paraffin in the blends with increasing of PE content. Thermal conductivity and leakage test results were also compared.