Reaction Propagation of Four Nanoscale Energetic Composites (Al/MoO3, Al/WO3, Al/CuO, and B12O3)
01 Jul 2007-Journal of Propulsion and Power (American Institute of Aeronautics and Astronautics (AIAA))-Vol. 23, Iss: 4, pp 707-714
TL;DR: In this article, the authors examined the performance of four different nanoaluminum/metal-oxide composites in terms of pressure output and propagaton speed for the open burn experiment and found that there is a correlation between the maximum pressure output of each composite and optimum propagation speed.
Abstract: Nanoscale composite energetics (also known as metastable intermolecular composites) represent an exciting new class of energetic materials. Nanoscale thermites are examples of these materials. The nanoscale thermites studied consist of a metal and metal oxide with particle sizes in the 30-200 nm range. They have potential for use in a wide range of applications. The modes of combustion and reaction behavior of these materials are not yet well understood. This investigation considers four different nanoaluminum/metal-oxide composites. The same nanoscale aluminum was used for each composite. The metal oxides used were molybdenum oxide (MoO 3 ), tungsten oxide (WO 3 ), copper oxide (CuO), and bismuth oxide (Bi 2 O 3 ). The reaction performance was quantified by the pressure output and propagation velocity using unconfined (or open burn) and confined (burn tube) experiments. We examine the optimization of each composite in terms of pressure output and propagaton speed (or burn rate) for the open burn experiment. We find that there is a correlation between the maximum pressure output and optimum propagation speed (or burn rate). Equilibrium calculations are used to interpret these results. We find that the propagation speed depends on the gas production and also on the thermodynamic state of the products. This suggests that condensing gases or solidifying liquids could greatly enhance heat transfer. We also vary the density of these composites and examine the change in performance. Although the propagation wave is likely supersonic with respect to the mixture sound speed, the propagation speed decreases with density. This behavior is opposite of classical detonation in which propagation (detonation) speed increases with density. This result indicates that the propagation mechanism may differ fundamentally from classical detonations.
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References
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TL;DR: In this paper, laser ignition experiments were performed to determine the ignition time of nanoscale particle diameter composites of aluminum (Al) and molybdenum trioxide (MoO3), which ranged from 17.4 nm to 20 μm.
344 citations
TL;DR: In this article, the behavior of composite systems composed of aluminum (Al) and molybdenum trioxide (MoO3) were studied as a function of Al particle size, equivalence ratio and bulk density.
Abstract: Combustion behavior of energetic composite materials was experimentally examined for the purpose of evaluating the unique properties of nano-scale compared with traditional micron-scale particulate media. Behavior of composite systems composed of aluminum (Al) and molybdenum trioxide (MoO3) were studied as a function of Al particle size, equivalence ratio and bulk density. Samples were prepared by mechanically mixing individual fuel and oxidizer particles and combustion experiments included measurements of ignition and flame propagation behavior. Ignition was achieved using a 50-W CO2 laser and combustion velocities were measured from photographic data. Reaction kinetics were studied with differential scanning calorimetry (DSC). Results indicate that the incorporation of nano-Al particles (1) significantly reduces ignition temperatures and (2) produces unique reaction behavior that can be attributed to a different chemical kinetic mechanism than observed with micron-Al particles.
303 citations
TL;DR: In this paper, combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions.
Abstract: Combustion velocities were experimentally determined for nanocomposite thermite powders composed of aluminum (Al) fuel and molybdenum trioxide (MoO3) oxidizer under well-confined conditions Pressures were also measured to provide detailed information about the reaction mechanism Samples of three different fuel particle sizes (44, 80, and 121nm) were analyzed to determine the influence of particle size on combustion velocity Bulk powder density was varied from approximately 5% to 10% of the theoretical maximum density (TMD) The combustion velocities ranged from approximately 600 to 1000m∕s Results indicate that combustion velocities increase with decreasing particle size Pressure measurements indicate that strong convective mechanisms are integral in flame propagation
270 citations
TL;DR: In this article, the authors used backscattering spectrometers, thermogravimetric analysis, and high-resolution transmission electron microscopy to investigate the oxidation behavior of ultrafine grain aluminum powder.
Abstract: Rutherford backscattering spectrometry, thermogravimetric analysis, and high‐resolution transmission electron microscopy were used to investigate the oxidation behavior of ultrafine grain aluminum powder. Fractional change in mass of Al powder samples were obtained as a function of temperature and exposure time for samples with different particle size distributions. As expected from surface energy considerations, the activation energy for oxidation of ultrafine grain particles is less than that for nominally flat surfaces. Activation energy for oxidation of powder samples with average particle diameters from 240 to 650 A was determined to be 0.5 eV, which is smaller than the value of 1.7 eV known for flat Al samples.
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TL;DR: In this article, three reactant synthesis techniques were examined; two focus on sol-gel processing of nanoscale Fe 2 O 3 particles and the third utilizes commercially available nanoscal Fe 2O 3 powder.
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