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Symposium : D
Nano-scale energetic materials: fabrication, characterization and molecular modeling
| start at | Subject | Num. |
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| Nanothermite : characterization techniques and new performances : to be defined | ||
| 09:00 | New Frontiers in Nanoenergetics Authors : Michael R. Berman Air Force Office of Scientific Research 875 N. Randolph St. Arlington, VA 22203, USA Resume : Novel chemical behavior can arise in nanoscale systems due to size and confinement effects on electronic structure and due to unique geometric structures. Detailed experiments coupled with atomistic and molecular modeling can help elucidate the properties of these materials and help design systems that can be used to improve storage and utilization of energy. The chemistry of novel nanostructured materials with unique reactivity and catalytic properties will be discussed in the context of their potential contribution to future applications in nanoenergetics. In particular, the size-selected reactivity of nanoclusters of aluminum with water will be discussed. In addition, the use of nanoscale catalysts to improve the performance of combustion systems will also be described. | 3 1 |
| 09:25 | Probing Reaction Dynamics in Nanothermites Authors : Michael R. Zachariah University of Maryland, College Park, MD, USA Resume : Nanoscale particles composed of a metal and metal oxide can undergo a violent thermite reaction. In these studies we probe with time resolved mass-spectrometry and optical emission the speciation and reaction dynamics of these materials. Species of Al, Al2O, and metals from the oxidizer were identified in mass spectra as reaction products. O2 released from the decomposition of oxidizer particles was also observed during the course of the thermite reactions. We find a correlation between the onset temperature of O2 release, and the ignition temperature suggesting that the formation of oxygen from oxidizer particles may be the important factor. An ignition delay is also observed from both optical and mass-spectrometry measurements. The delay increased with increase in shell thickness of the oxide on aluminum nanoparticles implying a diffusion mechanism, and from which an effective solid-state diffusion coefficient can be extracted. Using classical molecular dynamics simulations we have simulated the mechanochemical behavior of oxide coated aluminum nanoparticles. The results show that the high temperature oxidation process is driven by the electric field present in the oxide layer and accounts for approximately 90% of the mass flux of aluminum ions through the oxide shell. This result is consistent with the very interesting observation that the thermite event leads to a very short < 100 us current pulse of ions at superthermal energies. | 3 2 |
| 09:50 | Exothermic Reactions in Foils and Particles with Nanoscale Layering Authors : Timothy P. Weihs Professor Department of Materials Science and Engineering Johns Hopkins University Baltimore, MD, 21218 Resume : Energetic materials with nanoscale dimensions offered exciting opportunities for enhancing rates of reaction and hence energy delivery. However, characterizing the ignition thresholds, reaction rates and long-term stability of these materials can be challenging due to surface contamination, variations in particle size, or variations in reactant spacing. The use of layered materials with uniform and consistent reactant spacing provides model geometries for studying the properties of many exothermic reactions. This presentation reviews our studies of self-propagating exothermic reactions in materials with nanoscale layering. Using a combination of ignition experiments, velocity and temperature measurements, and continuum modeling we have identified many of the physical parameters that control ignition and the propagation of the reactions in sheet or foil form. We will also present studies of the same reactions in particle form, where convective heat transport can be important. Lastly, we will present our efforts to understand how the reactants combine and transform to the final products using in situ X-ray diffraction experiments. | 3 3 |
| 10:15 | COFFEE BREAK | |
| 10:30 | Impact Initiated Reactions in Intermetallic-forming Energetic Materials: Instrumented Experiments and Meso-Scale Simulations Authors : Naresh Thadhani School of Materials Science and Engineering Georgia Institute of Technology, Atlanta, Georgia Resume : The initiation of reactions in intermetallic-forming energetic materials (powder mixtures, compacts, and laminates) under uniaxial-strain and uniaxial-stress impact loading with the gas gun will be discussed. The discussion will be based on the use of time-resolved instrumented experiments combined with meso-scale numerical simulations. Instrumented experiments, employing stress gauges, velocity interferometry, and high-speed digital imaging to measure the stress profiles, shock velocity, and transient deformation states, provide evidence of reaction initiation at varying time scales. Meso-scale simulations of wave propagation through discretely represented constituents (with real imported microstructures) is performed using the multi-material CTH Eulerian code to investigate the effects of reactant morphology on the deformation and mixing in the powder mixtures, compacts, and foils. Observations of particle level processes reveal the heterogeneous nature of effects of wave propagation through the reactants of dissimilar physical and mechanical properties, as well as the various morphological characteristics. The resulting localized flow, jetting, and vortex formation, contribute to the mixing of reactants and subsequent reaction initiation. The information generated is useful for understanding the reaction mechanisms and controlling the characteristics of their initiation and resulting energy release.
Funded by ONR-MURI Grant No. N00014-07-1-0740. | 3 4 |
| 10:55 | Energetic thermites mechanical behaviour : the nano-scale effects Authors : Peggy LAMY-BRACQ, Nexter Munitions Resume : Compression behaviour of energetic composite materials was experimentally examined in order to evaluate the unique properties of nano-scale compared with traditional micron-scale particulate media. Porosity and mechanical resistance have an important effect on the final behaviour of energetic material during the solid-state combustion. They govern the reaction surface the pellet develops. Behaviours of metastable intermolecular composites composed of aluminum and metal-oxides were studied. A quasi-chemical model is used to understand the special mode of compression of the nano-scale material. This modelisation makes it possible to formulate compositions with a controlled porosity for a sufficient mechanical resistance. The use of nano-scale media allows reaching a higher porosity for the same cohesion that micron-scale ones. It\'s a way to control the combustion velocities. | 3 5 |
| 11:15 | Synthesis and characterization of self-assembled nanoenergetic Al-Fe2O3 thermite system Authors : J.L. CHENG , H. H. HNG School of Materials Science & Engineering, Nanyang Technological University, Singapore X. Y. NG , P. C. SOON , Y. W. LEE DSO National Laboratories, Singapore Resume : Synthesis and characterization of self-assembled nanoenergetic Al-Fe2O3 thermite system
J.L. CHENG, H. H. HNG
School of Materials Science & Engineering, Nanyang Technological University, Singapore
X. Y. NG, P. C. SOON, Y. W. LEE
DSO National Laboratories, Singapore
Nanoenergetic powders have superior exothermic characteristics and possess properties unobtainable by traditional energetic materials. One class of nanoscale metal-based energetic materials consists of nanosized aluminum and metal oxides. This type of material is frequently named as superthermites or metastable intermolecular composites. The energy released in redox reactions of thermite energetic materials depends on the arrangement of the oxidizer and fuel. In many cases, this reaction is a solid-state diffusion driven process depending mainly on the interfacial contact area between the oxidizer and the fuel, and an increase in this interfacial area will result in an enhanced rate of energy release. The efforts made so far in energetic thermite system usually involves physical random mixing of the oxidizer and fuel leading to inhomogeneous distribution, and thus lesser interfacial area of contact.
The work presented is concerned with the synthesis and characterization of nanoenergetic superthermites with the goal of attaining distinctive ordered network morphologies, therefore resulting in enhanced exothermic heats of reaction. In light of past developments, we have attempted an approach to produce nanostructured superthermites (Al and Fe2O3) by self-assembly methods to achieve molecular level self assembly whereby the fuel nanoparticles are arranged in an orderly and controlled manner around the oxidizer and vice-versa. The ordered composition results in maximum interfacial contact area between the fuel and oxidizer, and hence attaining higher energy released at a very fast rate. Morphology of the thermite system also played an important role in enhancing combustion kinetics. A novel combination of Fe2O3 nanotubes and spherical nano Al particles was chosen and synthesized to further increase the effective surface area of combustion. Preliminary results are promising, and significant improvements in energetic capabilities have been demonstrated. Maximum pressure rise, rate of energy release, ignition temperature and ignition delay time have been improved by a few folds in the self-assembled samples as compared to mechanically mixed samples. | 3 6 |
| 11:35 | Synthesis processes of nanostructured energetic material Al/CuOx: nanowires and multilayers on substrate Authors : M. Petrantoni1,2, C. Rossi1,2, V. Conédéra1,2, L. Salvagnac1,2, D. Bourrier1,2, C. Tenailleau3, P. Alphonse3, J. Y. Chane-Ching3 1 CNRS ; LAAS ; 7 avenue du colonel Roche, F-31077 Toulouse, France 2 Université de Toulouse ; UPS, INSA, INP, ISAE ; LAAS ; F-31077 Toulouse, France 3 CIRIMAT, 118 route de Narbonne, 31062 Toulouse Cedex 04, France Resume : Nanowires growth and multilayers deposition of energetic material Al/CuOx are two microelectronic processes which are developed to integrate on-board energy sources on microsystems. Al/CuO is a composite material which exhibits very exothermic reaction (21kJ/cm3) and large reaction rate.
Nanowires come from thermal oxidation of copper thin film on silicon substrate at 450°C during 5 hours. The value of heating and cooling rates is 2°C/min to avoid higher temperature change of the sample and to obtain only one kind of copper oxide: CuO. Multilayers are made by magnetron sputter deposition. These two nanostructures (nanowires and multilayers) lead to a good intimacy between the oxidizer (CuOx) and fuel (Al), the diffusion distances between reactants are decreased and the specific area is increased. So, ignition delay and power are reduced.
Nanostructured CuOx/Al material is then integrated onto a micro heater made of Au/Pt/Cr on pyrex substrate to make characterization of the thermite ignition. In the case of nanowires, we get an ignition power and delay of 1.16 W and 0.2 ms respectively. The energy release is 10kJ/cm3. This value may be improved by studying the reactants stoichiometry.
This work has demonstrated the feasibility of the energetic material integration in microelectronics, the reproducibility and the material performances. | 3 7 |
| 12:00 | LUNCH BREAK | |
| Explosive and pyrotechnics : characterization techniques and new performances : to be defined | ||
| 14:00 | Novel Catalytic Behavior of Water in High Explosive Decomposition Authors : Christine J. Wu, Laurence E. Fried*, Lin H. Yang, Nir Goldman and Sorin Bastea Lawrence Livermore National Laboratory L-282 P. O. Box 808 7000 East Avenue Livermore, CA 94550 Resume : Water under conditions of extremely high pressure and temperature is known to exhibit fascinating physical behaviors. Its remarkable structural and phase complexity strongly suggests that its chemical properties, which are largely unstudied, may be unusual as well. Detonations of high explosives containing oxygen and hydrogen provide unique systems for exploring the chemistry of “extreme water”, because detonations form water at conditions similar to those of giant planetary interiors. Contrary to the current view of water as a stable final product, we show here that water plays an unexpected role in catalyzing complex explosive reactions. From first-principles atomistic simulations of the high explosive pentaerythritol tetranitrate (PETN), we discovered that H2O (source), H (reducer) and OH (oxidizer) act as a dynamic team that transports oxygen between reactive centers. Our finding suggests that H2O may catalyze reactions in other explosives and in planetary interiors. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. | 4 1 |
| 14:25 | Sol-gel Synthesis of Nano-composite Crycrstalline HMX/AP Coated by Resorcinol-formaldehyde Authors : NIE Fu-de ZHANG Juan GUO Qiu-xia QIAO Zhi-qiang ZENG Gui-yu (Institute of Chemical Materials, CAEP, Mianyang, 621900, China) Resume : The object of this work is to try to improve the performance of composite explosive by using sol-gel method to mix high explosive and oxidizer in nanoscale. Nano-composite materials of HMX and AP were prepared by using resorcinol-formaldehyde (RF) as binder. Its structure was characterized by scanning electron microscopy (SEM), BET method, X-ray powder diffraction (XRD), and DSC. SEM indicates that HMX/AP/RF aerogel is laminate-like structure with uniform aperture. The XRD results show that the mean crystal size of HMX is less than 100nm; HMX and AP are mixed uniformly in nanoscale. The specific surface area of HMX/AP/RF is 27m2/g and much less than that of RF aerogel, whose mesopores and micropores mainly focus in the range of 2-20nm and 0.6-1.6nm respectively. DSC indicates that the thermal decomposition temperature of HMX/AP/RF is reduced by 27℃ compared to original HMX. | 4 2 |
| 14:45 | NANOSIZE MATERIALS AND HIGH-ENERGY CONDENSED SYSTEMS Authors : Yurii Frolov Semenov Institute of Chemical Physics, Russian Academy of Science 119991Kosygin st., Moscow, Russia Resume : The promising use of nanoscale materials as components of high-energy
condensed systems to increase its efficiency arises some problems to be
decided. Namely, they are: synthesis technology development, chemical
stabilization for safe handling and storage, novel properties and
parameters need to be measured in a nano-scale, introduction of
nanocomponents into the matrix to produce composite material, etc. To
solve these tasks the novel complex approach and adequate equipment are to
be applied. In general, the microstructure of high-energy Heterogeneous
Condensed Systems (HCS) strongly depends on the component’s size, which in
turn is reflected on the combustion and detonation parameters. Present
article is focused on some synthesis techniques to produce energetic
nanomaterials (nitramines, metals, metal oxides). Properties of these
materials are discussed, including the high-temperature behavior.
Combustion parameters (burning rate, particle size agglomeration) are
determined and compared to compositions with micron- scale components. It
is underlined, that the final conclusion about perspectives and the most
promising directions of the nanosized materials development in the field
of HCS requires additional experimental, theoretical study, and new
information, which will be increased by the income of this conference. | 4 3 |
| 15:10 | Energetic nanomaterials: opportunities for enhanced performances Authors : Denis Spitzer, Marc Comet, Christian Baras, P. Lehmann Resume : This paper will deal with the contribution of the nanomaterials to the contemporary pyrotechnics science. The breakthroughs in this domain will be illustrated by several examples of energetic nanomaterials recently studied in our laboratory.
The solidification of energetic phases in a porous matrix (Cr2O3) was used to prepare and to stabilize at nanoscale explosive particles (RDX). The thermochemical behaviour of RDX nanoparticles strongly differs from the one of micron-sized RDX. For instance, the temperature at which the decomposition occurs is significantly lowered and the melting point is apparently removed. The effect of the decomposition of RDX nanoparticles on the matrix in which they are trapped was observed for the first time by Atomic Force Microscopy (AFM).
The Cr2O3/RDX nanocomposite materials were mixed with aluminium nanoparticles in order to formulate Gas Generating Nanothermites (GGNT). The combustion of GGNT is unique because it involves a synergy mechanism in which the decomposition of RDX nanoparticles fragments the Cr2O3 matrix and primes the thermite reaction.
“Classical” nanothermites were obtained by mixing nanoparticles (diameter < 100 nm) of metallic oxides (WO3, MnO2) with a reducing metal (Al). These materials were used to demonstrate that nanoparticles (i) significantly lower the ignition delay time and (ii) remarkably increase the combustion rate.
Finally, pure RDX nanoparticles can be prepared by a continuous process of crystallization. Thermal driven AFM showed the decreasing of the melting point temperature which is of great interest for the industrial processing of this explosive. | 4 4 |
| 15:35 | COFFEE BREAK | |
| 15:50 | Characterization of Explosives Traces by the Nanocalorimetry Authors : N. Piazzon 1, 2, M. Rosenthal 1, A. Bondar 1, D. Spitzer 2, D.A. Ivanov 1 1 Institut des Sciences des Matériaux de Mulhouse, IS2M, CNRS LRC 7228, 15 rue Jean Starcky, 68057 Mulhouse, France 2 Institut franco-allemand de recherches de Saint-Louis (ISL), 68301 Saint-Louis, France Laboratoire ISL/CNRS Nanomatériaux pour les Systèmes Sous Sollicitations Extrêmes (NS3E) UMR 3208 CNRS Resume : Thermal characterization of energetic materials is a non-trivial task. Differential scanning calorimetry on such materials have been mainly performed using special high pressure crucibles, in which the pressure uncontrollably changes during the measurement. Performing constant pressure experiments would allow addressing the kinetics of the decomposition reaction more quantitatively. Another practical application related to the explosives detection requires characterizing much smaller samples such as nano-grams to pico-grams, which correspond to the explosives in the state of traces.
In our laboratory, we have built a Nanocalorimeter, which can safely measure nano-gram-size samples using extremely high heating rates (103 to 1 million K/s). Similar to the setups described in the literature, our Nanocalorimeter is based on a commercial gas detector sensor with integrated heating elements and thermocouples. The device is operational in DC and AC modes, with the temperature modulation frequencies as high as 3.0-10.0 kHz.
In this work, we have characterized for the first time a series of energetic materials of practical interest. The samples have been deposited on the sensor membrane using either micro-manipulation or spin-coating. The mass of the sample was determined from its heat capacity measured in both operational modes. Coupling the Nanocalorimeter to a fast CCD camera was found quite useful to simultaneously visualize the processes occurring on a micro-second time-scale. | 4 5 |
| 16:15 | SYNTHESIS AND CHARACTERIZATION OF ENERGETIC NANOMATERIALS Authors : A.E.D.M. van der Heijden, Y.L.M. Creyghton, E. Abadjieva Resume : Nanomaterials are a topic of increased interest, since they have properties which differ from their macroscopic counterparts. Many applications nowadays take advantage of the new functionalities which natural and manufactured nanoparticles possess. Based on these developments, also the research on energetic nanomaterials is receiving more and more attention. Apart from the synthesis of energetic nanomaterials, another area of interest is the coating of energetic (nano)powders, in order to be able to modify their properties or to add new functionalities to these particles. (Modified) energetic materials may find applications in explosives, gun and rocket propellants and pyrotechnic devices. Enhanced properties are expected e.g. a lower vulnerability towards shock initiation, enhanced blast, enhanced shelf life and environmentally friendly replacements of currently used materials.
At TNO Defence, Security and Safety experimental set-ups for the synthesis of energetic nanomaterials as well as for coating of existing powders have been designed and constructed. The experimental technique is based on a special plasma application which, contrary to more general plasmas, can be operated at relatively low temperatures and ambient pressure. This allows the handling (synthesis and treatment) of heat-sensitive materials, which would otherwise readily decompose or react at higher temperatures. The facility used for the coating of energetic powders in the lower micron range is based on a fluidized bed reactor in which the powder circulates.
In this paper the experimental techniques will be described and examples will be given of nano-RDX as well as other materials that have been produced and characterized. | 4 6 |
| 16:35 | Recent advances in the field of nano-sized powder based-energetic materialsRecent advances in the field of nano-sized powder based-energetic materials Authors : C. Perut, G. Lacroix, O. Orlandi and C. Collet SNPE Mateaux Energeques Centre de Recherches du Bouchet (CRB) 9, rue Lavoisier, 91710 Vert-Le-Petit, France Resume : Nanotechnolgy is considered as promising for contributing to reach the main objectives of research and development efforts for explosives and solid rocket propellants which are to increase performances and to improve responses to unplanned stimuli (Insensitive Munitions). This paper will address different aspects related to the manufacture, the characterization and the use of ultra-fine or nano-sized aluminium and energetic ingredients. The mean diameters of aluminium particles are in the range 80 – 300 nm according to the samples. The particles are passivated by an oxide layer. Characterization by TEM and local chemical analysis have shown that alumina is amorphous and its thickness is around 2 nm. Adequate dispersion of ultra-fine particles in an energetic material is quite a challenge. This may be achieved by composition and mixing process optimization as it is shown by TEM visualization. Replacement of micron-sized aluminium by ultra-fine particles in HTPB/AP/Al propellants leads to an increase around 80% of the burning rate. This change in explosive formulations induces a lowering in the detonation velocity and a decrease of overpressures and temperatures during the afterburning phase with air. Hypothesis to explain this behaviour will be discussed in this paper.
It is reported by literature that the shock sensitivity depends on nitramine particle diameter for nitramine/HTPB high explosive and nitramine/AP/HTPB solid propellants. Extrapolation of this behaviour seems to indicate an interest for nano-sized particles. So, numerous researcher teams are working on the ways to realize them. Two technologies are assessed, milling and crystallization. The results obtained in this field will be presented. | 4 7 |
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