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Michelle L Pantoya – One of the best experts on this subject based on the ideXlab platform.

  • ThermAl anAlysis of microscAle Aluminum Particles coated with perfluorotetradecanoic (PFTD) acid
    Journal of Thermal Analysis and Calorimetry, 2020
    Co-Authors: Loudon L. Campbell, Dylan K. Smith, Kevin J. Hill, Michelle L Pantoya
    Abstract:

    Micron-diameter Aluminum Particles (μAl) are highly reactive when combined with a solid oxidizer. However, μAl powder is less reactive in a gaseous air environment, where oxygen is the only available oxidizer, unless very well dispersed. While enthAlpy of oxidation for Al is high, many variables influence the viability of harnessing stored chemicAl energy within a single Al Particle whose reaction is diffusion controlled. One way to enhance Al Particle reaction is to coat the Particle surface with a condensed phase oxidizing agent that is in immediate contact with the Particle surface to promote diffusion reactions. Fluorocarbons such as perfluorocarboxylic acids have been used to enhance Al combustion for nanoscAle Al (nAl) Particles because fluorinated species are Also reactive with the Al_2O_3 passivation shell surrounding the Al core Particle. This study extends previous work on nAl toward μAl Particles coated with perfluorotetradecanoic acid (PFTD) (F_3C(CF_2)_11CO_2H) and then characterizes the μAl-PFTD thermAl reactivity. Samples were prepared with varying PFTD concentrations ranging from 0 to 20 mass percent, and experiments were performed using thermogravimetric anAlysis and high-speed infrared imaging on powder samples. Results show the PFTD-coated μAl Particles provide higher apparent reaction temperatures (by about 500 °C) and longer burn times at elevated temperatures (by about 20%). Higher concentrations of PFTD tend to produce more gas-generating reactions with Particles ejecting from the loose powder pile, but 9% PFTD coating on μAl Particles provides a good bAlance of stable reactivity with high-temperature reactions (~ 1800 °C) and high-temperature burn times (~ 18 s). The higher temperatures for PFTD-coated μAl Particles are attributed to the increased (nearly double) energy produced in the formation of AlF_3 (56.10 kJ g^−1) compared to Al_2O_3 (30.98 kJ g^−1); both of these product species are identified in XRD anAlysis. In addition, the formation of AlF_3 may reduce the melting and phase transition temperature of Al_2O_3 by severAl hundred degrees and contribute to catAlyticAlly activating the Al reaction. OverAll, coating μAl Particles with a fluorinated polypolymer facilitates reaction in an air environment, even for smAll concentrations of PFTD coating.

  • On the possible coexistence of two different regimes of metAl Particle combustion
    Combustion and Flame, 2020
    Co-Authors: Igor Altman, Andrew R. Demko, Kevin J. Hill, Michelle L Pantoya
    Abstract:

    Abstract The coexistence of two regimes of Aluminum (Al) Particle combustion is discussed. A slower regime occurs at a low energy accommodation coefficient (EAC) and is usuAlly observed in Al combustion experiments. A faster regime at high EAC is Also possible. The combustion enhancement observed for pre-treated Al Particles can be interpreted as a switch from the slower combustion regime to the faster regime. The vAlue of EAC is controlled by the thermionic emission of electrons. A relationship between Al Particle pre-treatment and the work function, which governs the thermionic emission, and, therefore, the EAC, is a subject of further studies.

  • A slice of an Aluminum Particle: Examining grains, strain and reactivity
    Combustion and Flame, 2016
    Co-Authors: Jena Mccollum, Michelle L Pantoya, Kevin J. Hill, Dylan K. Smith, Juliusz Warzywoda, Nobumichi Tamura
    Abstract:

    Abstract Micron-scAle Aluminum (Al) Particles are plagued by incomplete combcombustion that inhibits their reactivity. One approach to improving reactivity is to anneAl Al Particles to increase dilatationAl (volumetric) strain which has Also been linked to increased combustion performance. While optimAl anneAling temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on Particle combustion performance. This study examines the effect of quenching after anneAling Al microParticles to 100, 200 and 300 °C on intra-Particle dilatationAl strain and reactivity. Synchrotron X-ray diffraction anAlysis of the Particles reveAls the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatationAl strain of the Aluminum-core, Alumina-shell Particles. The anneAled and quenched Al Particles were then combined with a metAl oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a criticAl anneAling temperature of 300 °C is reached and performance is maintained for each anneAling temperature regardless of cooling rate. These results show that Altering the mechanicAl properties and combustion performance of Al Particles is strongly dependent on the anneAling temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic defodeformation mechanisms on strain are Also considered and additionAl experimentAl results are shown on the microstructure of an Al Particle. Focused ion beam milling of an Al Particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al Particles. This confirmed that the Al microParticles have a polycrystAlline structure shown by grains All exceeding 100 nm in size.

Zhen-yan Deng – One of the best experts on this subject based on the ideXlab platform.

  • Effect of initiAl gas pressure on the reaction of Al with water
    International Journal of Hydrogen Energy, 2014
    Co-Authors: Wei-zhuo Gai, Zhen-yan Deng
    Abstract:

    Abstract The effect of initiAl gas pressure on Al–water reaction was investigated systematicAlly. It was found that there is a non-monotonic relationship between the initiAl pressure and the induction time for the beginning of Al–water reaction. The induction time decreases with decreasing the initiAl pressure at the first stage from atmospheric pressure, then reaches a minimum, and finAlly increases with further decreasing the initiAl pressure. The mechanism anAlyses reveAled that the speciAl vacuum pressure corresponding to the minimum induction time is close to the saturated vapor pressure, below which probably there are some vapor bubbles passing or adsorbing on Al Particle surfaces due to boiling, retarding the hydration process of Al surface oxidoxide film and increasing the reaction induction time. The present results imply that a suitable initiAl gas pressure should be chosen for Al–water reaction to generate hydrogen.

  • reaction of Al powder with water for hydrogen generation under ambient condition
    International Journal of Hydrogen Energy, 2012
    Co-Authors: Wei-zhuo Gai, Zhen-yan Deng, Wenhui Liu, Jiange Zhou
    Abstract:

    Abstract Hydrogen-generation by the reaction of pure Al powder with deionized water under ambient condition was investigated systematicAlly. The results showed that both nano- and micro-sized Al powders could react with water and generate hydrogen under ambient pressure at mild temperature. The nanometer Al powder Almost completely reacted with water at 20 °C, most of micrometer Al powders could react with water at a temperature of >40 °C, implying that smAll-sized Al powder could directly be able to generate hydrogen without any activation or modification. A shrinking core model was used to anAlyze the reaction progress, indicating that the Al-water reaction was controlled by the surface chemicAl mechanism at the initiAl stage, and then by the H2O molecule diffusion in the byproduct layer afterwards. The activation energy was cAlculated, which increased from 64.2 kJ/mol to 88.7 kJ/mol with increasing the Al Particle sizes from 98.38 nm to 24.94 μm. X-ray anAlyses reveAled that the reaction byproducts are bayerite, boehmite or a mixture of them, depending on the reaction temperature. The reaction dynamics mechanisms are discussed.

  • Role of Particle Sizes in Hydrogen Generation by the Reaction of Al with Water
    Journal of the American Ceramic Society, 2010
    Co-Authors: Zhen-yan Deng, Yoshio Sakka, Li-li Zhu, Ye-bin Tang, Rong-jun Xie
    Abstract:

    Four different-sized pure Al powders were used to react with distilled water at 55°C in a low vacuum, and their effect on the reaction dynamics and hydrogen-generation rate was investigated. It was found that the Al Particle sizes not only affect the hydrogen-generation rate but Also affect the induction time for the beginning of the reaction. The induction time strongly depends on the Al Particle sizes, which obviously increased with the Al Particle sizes. The hydrogen-generation rate increased with the decreasing Al Particle sizes, because the smAll-sized Al powder has a high surface area. Mechanism anAlyses reveAled that the long induction time for the large Al Particles probably originates from a long time for their H diffusion to reach a saturation concentration in the bulk Al metAl. The reaction rate of Al with water could be quAlitatively explained by a shrinking core model.

Yoshio Sakka – One of the best experts on this subject based on the ideXlab platform.

  • Role of Particle Sizes in Hydrogen Generation by the Reaction of Al with Water
    Journal of the American Ceramic Society, 2010
    Co-Authors: Zhen-yan Deng, Yoshio Sakka, Li-li Zhu, Ye-bin Tang, Rong-jun Xie
    Abstract:

    Four different-sized pure Al powders were used to react with distilled water at 55°C in a low vacuum, and their effect on the reaction dynamics and hydrogen-generation rate was investigated. It was found that the Al Particle sizes not only affect the hydrogen-generation rate but Also affect the induction time for the beginning of the reaction. The induction time strongly depends on the Al Particle sizes, which obviously increased with the Al Particle sizes. The hydrogen-generation rate increased with the decreasing Al Particle sizes, because the smAll-sized Al powder has a high surface area. Mechanism anAlyses reveAled that the long induction time for the large Al Particles probably originates from a long time for their H diffusion to reach a saturation concentration in the bulk Al metAl. The reaction rate of Al with water could be quAlitatively explained by a shrinking core model.

  • modification of Al Particle surfaces by γ Al2o3 and its effect on the corrosion behavior of Al
    Journal of the American Ceramic Society, 2005
    Co-Authors: Zhen-yan Deng, Yu-fu Liu, Yoshihisa Tanaka, Yoshio Sakka
    Abstract:

    MetAl Al Particle surfaces were modified by fine γ-Al2O3 grains using a mixture of Al and Al(OH)3 powders, which was pressureless sintered at a temperature of 600°C in vacuum. All the constituents on originAl Al Particle surfaces were transformed into γ-Al2O3 phase after sintering. No dense passive oxide layers on Al Particle surfaces were formed even after the modified Al Particles were exposed to oxidation environment. The modified Al Particles could continuously react with pure water and generate hydrogen at room temperature. The present finding implies that metAl Al could become hydrogen-generation materiAl by surface modification.

  • Modification of Al Particle Surfaces by γ‐Al2O3 and Its Effect on the Corrosion Behavior of Al
    Journal of the American Ceramic Society, 2005
    Co-Authors: Zhen-yan Deng, Yu-fu Liu, Yoshihisa Tanaka, Yoshio Sakka
    Abstract:

    MetAl Al Particle surfaces were modified by fine γ-Al2O3 grains using a mixture of Al and Al(OH)3 powders, which was pressureless sintered at a temperature of 600°C in vacuum. All the constituents on originAl Al Particle surfaces were transformed into γ-Al2O3 phase after sintering. No dense passive oxide layers on Al Particle surfaces were formed even after the modified Al Particles were exposed to oxidation environment. The modified Al Particles could continuously react with pure water and generate hydrogen at room temperature. The present finding implies that metAl Al could become hydrogen-generation materiAl by surface modification.

J. J. Granier – One of the best experts on this subject based on the ideXlab platform.

  • The role of the Al_2O_3 passivation shell surrounding nano-Al Particles in the combustion synthesis of NiAl
    Journal of Materials Science, 2004
    Co-Authors: J. J. Granier, K. B. Plantier, M. L. Pantoya
    Abstract:

    The self-propagating combustion behaviors of Nickel (Ni) and Aluminum (Al) thermites were studied as a function of bimodAl Al Particle size distributions. In particular, the low melting temperature of nano-scAle Al Particles coupled with the low concentrations of Al_2O_3 in micron-scAle Al Particles were exploited in order to optimize the macroscopic properties of the finAl Alloy. BimodAl Al size distributions ranging from 0 to 50 wt% nano-Al combined with 50 wt% Ni were studied. Laser ignition experiments were performed on pressed pellets to determine flame propagation behavior and product microstructurAl features as a function of Al Particle size. A new imaging technique is Also presented that Allows visuAlization of the surface reaction through highly luminescent flames and more accurate evAluation of burn rates. The wear behavior of the product Alloy was measured and reported. Results show that composites composed of more micron-scAle than nano-scAle Al Particles absorb more laser energy prior to flame propagation and experience an effective preheating. When 10–30 wt% nano Al is combined with micron Al and Ni, the wear resistance of the product Alloy is optimized. Electron micrographs of the Alloys suggest these properties may be attributed to whisker formations that behave as binding strings improving the overAll abrasion resistance of the composite.

  • The role of the Al2O3 passivation shell surrounding nano-Al Particles in the combustion synthesis of NiAl
    Journal of Materials Science, 2004
    Co-Authors: J. J. Granier, K. B. Plantier, Michelle L Pantoya
    Abstract:

    The self-propagating combustion behaviors of Nickel (Ni) and Aluminum (Al) thermites were studied as a function of bimodAl Al Particle size distributions. In particular, the low melting temperature of nano-scAle Al Particles coupled with the low concentrations of Al2O3 in micron-scAle Al Particles were exploited in order to optimize the macroscopic properties of the finAl Alloy. BimodAl Al size distributions ranging from 0 to 50 wt% nano-Al combined with 50 wt% Ni were studied. Laser ignition experiments were performed on pressed pellets to determine flame propagation behavior and product microstructurAl features as a function of Al Particle size. A new imaging technique is Also presented that Allows visuAlization of the surface reaction through highly luminescent flames and more accurate evAluation of burn rates. The wear behavior of the product Alloy was measured and reported. Results show that composites composed of more micron-scAle than nano-scAle Al Particles absorb more laser energy prior to flame propagation and experience an effective preheating. When 10–30 wt% nano Al is combined with micron Al and Ni, the wear resistance of the product Alloy is optimized. Electron micrographs of the Alloys suggest these properties may be attributed to whisker formations that behave as binding strings improving the overAll abrasion resistance of the composite.

John J Granier – One of the best experts on this subject based on the ideXlab platform.

  • effect of bulk density on reaction propagation in nanothermites and micron thermites
    Journal of Propulsion and Power, 2009
    Co-Authors: Michelle L Pantoya, John J Granier, Valery I Levitas, Jack B Henderson
    Abstract:

    The thermite reaction of nanoscAle Aluminum and molybdenum trioxide Particles has reveAled a paradoxicAl relationship between Al Particle size and mixture bulk density. SpecificAlly, with micron-scAle Al Particles, the thermite demonstrates an expected growth in flame speed with increased density, but nanoscAle-AlParticle mixtures exhibit an opposing trend. This paper presents new experimentAl measurements of the thermAl properties of this thermite as a function of Al Particle size and applies a new oxidation mechanism in an effort to explain the paradoxicAl results between Al Particle size and mixture bulk density. Results show that the nanocomposite‘s behavior is consistent with a new melt-dispersion oxidation mechanism and convective mode of flame propagation. Compaction-induced damage of the oxide shell and distortion of the shape of sphericAl Particles, as well as reduced free space around Al nanoParticles suppress the melt-dispersion mechanism and reduce flame speed. An additionAl mode of energy transfer is proposed that is associated with molten Al clusters from the melt-dispersion mechanism that advance faster than the flame velocity. Micron-scAle Particle reactions may be governed by diffusion such that increased bulk density coincides with increased thermAl properties and increased flame speeds.

  • The effect of slow heating rates on the reaction mechanisms of nano and micron composite thermite reactions
    Journal of Thermal Analysis and Calorimetry, 2006
    Co-Authors: Michelle L Pantoya, John J Granier
    Abstract:

    ThermAl anAlyses were performed on Al+MoO3 thermite reactions as a function of Al Particle size (ranging from 50 to 20 μm) and heating rate (from 2.5 to 15 K min–1 ). Results include ignition (onset) temperatures and heats of reaction. The nano-thermites initiate prior to reactant phase changes and at least 300°C below micron-thermites. The differences in ignition temperatures are suggestive of different ignition mechanisms. Nano-thermites display higher heats of reaction that are dependent on experimentAl conditions.

  • combustion behavior of highly energetic thermites nano versus micron composites
    Propellants Explosives Pyrotechnics, 2005
    Co-Authors: Michelle L Pantoya, John J Granier
    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 micronAl Particles.