Reactive sintering: An important component in the combustion of nanocomposite thermites

Sullivan, Kyle T.; Piekiel, Nicholas W.; Wu, Chun-Wei; Chowdhury, Snehaunshu; Kelly, Stephen T.; Hufnagel, T. C.; Fezzaa, Kamel; Zachariah, Michael R.

doi:10.1016/j.combustflame.2011.07.015

Cited by 144 publications

(107 citation statements)

References 51 publications

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“…Recent advances in particle production techniques have brought fuel particle sizes down to the nano-scale, and many have shown that Al nanoparticles (nAl) exhibit higher reactivity than Al microparticles (µAl). There are several potential mechanisms explaining the increase in reactivity for nAl [8][9][10][11][12][13][14][15][16]. However, interest is now shifting towards utilizing what is understood about the mechanisms promoting optimal reactivity in nAl particles towards engineering more reactive µAl particles.…”

Section: Introductionmentioning

confidence: 99%

A slice of an aluminum particle: Examining grains, strain and reactivity

McCollum

Smith

Hill

et al. 2016

Combustion and Flame

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Micron-scale aluminum (Al) particles are plagued by incomplete combustion 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 o 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 deformation 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.

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Section: Introductionmentioning

confidence: 99%

A slice of an aluminum particle: Examining grains, strain and reactivity

McCollum

Smith

Hill

et al. 2016

Combustion and Flame

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“…Various explanations for Al oxidation mechanisms have also been proposed, each strongly tied to the ignition mechanism and heating rate [3]- [11]. All theories share a common theme for mass transport of fuel and oxidizer, but differ in how that diffusion is achieved (i.e., via (a) dispersion [3], [4], (b) phase changes in the polymorphous passivation shell [5]- [7] , (c) reactive sintering [8], (d) pressure gradient driven processes [9], [10], and (e) induced electric field influences [11]). This article will not directly deal with any particular reaction mechanism, but rather investigate the influence of a new parameter, mechanical strain, which has only recently been considered in the study of Al oxidation [3], [4], [12], [13].…”

Section: Introductionmentioning

confidence: 99%

Improving aluminum particle reactivity by annealing and quenching treatments: Synchrotron X-ray diffraction analysis of strain

2016

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In bulk material processing, annealing and quenching metals such as aluminum (Al) can relieve residual stress and improve mechanical properties. On a single particle level, affecting mechanical properties may also affect Al particle reactivity. This study examines the effect of annealing and quenching on the strain of Al particles and the corresponding reactivity of aluminum and copper oxide (CuO) composites. Micron-sized Al particles were annealed and quenched according to treatments designed to affect Al mechanical properties. Synchrotron X-ray diffraction (XRD) analysis of the particles reveals the thermal treatment increased the dilatational strain of the aluminum-core, alumina-shell particles. Flame propagation experiments also show thermal treatments effect reactivity when combined with CuO. An effective annealing/quenching treatment for increasing aluminum reactivity was identified. These results show that altering the mechanical properties of Al particles affects their reactivity. This manuscript focuses on synchrotron x-ray diffraction analysis of aluminum particles that have been treated to improve their mechanical properties. The aluminum is then examined for its reactivity with a metal oxide to show the relationship between material processing and the mechanical properties of the metal then extend this understanding towards application for energy generation technologies. We felt this combination of in-depth analysis of the material property of strain based on annealing and quenching processing of a metal powder and its application to reactivity were the perfect combination of mechanical and functional behavior appropriate for Acta Materialia. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 AbstractIn bulk material processing, annealing and quenching metals such as aluminum (Al) can relieve residual stress and improve mechanical properties. On a single particle level, affecting mechanical properties may also affect Al particle reactivity. This study examines the effect of annealing and quenching on the strain of Al particles and the corresponding reactivity of aluminum and copper oxide (CuO) composites. Micron-sized Al particles were annealed and quenched according to treatments designed to affect Al mechanical properties. Synchrotron Xray diffraction (XRD) analysis of the particles reveals the thermal treatment increased the dilatational strain of the aluminum-core, alumina-shell particles. Flame propagation experiments also show thermal treatments effect reactivity when combined with CuO. An effective annealing/quenching treatment for increasing aluminum reactivity was identified. These resultsshow that altering the mechanical properties of Al particles affects their reactivity.

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“…Nanoscale Al fuel, despite a large surface to volume ratio, is limited by its comparatively large surface oxide layer, as well as rapid agglomeration effects when nanoparticles are ignited. 24 A macroscale material assembled from ligand-protected atomic aluminum clusters may offer a combination of extremely rapid oxidation kinetics as well as higher energy density than traditional organic fuels. The stability of these materials in ambient oxidizer, as well as the ability to scale up synthesis processes, are key challenges in utilizing this system as a pragmatic material.…”

Section: Introductionmentioning

confidence: 99%

Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

Alnemrat

Hooper

2014

The Journal of Chemical Physics

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Oxidation of ligand-protected aluminum clusters: an ab-initio molecular dynamics study. "J. Chem. Phys. 140, 104313 (2014 We report Car-Parrinello molecular dynamics simulations of the oxidation of ligand-protected aluminum clusters that form a prototypical cluster-assembled material. These clusters contain a small aluminum core surrounded by a monolayer of organic ligand. The aromatic cyclopentadienyl ligands form a strong bond with surface Al atoms, giving rise to an organometallic cluster that crystallizes into a low-symmetry solid and is briefly stable in air before oxidizing. Our calculations of isolated aluminum/cyclopentadienyl clusters reacting with oxygen show minimal reaction between the ligand and O 2 molecules at simulation temperatures of 500 and 1000 K. In all cases, the reaction pathway involves O 2 diffusing through the ligand barrier, splitting into atomic oxygen upon contact with the aluminum, and forming an oxide cluster with aluminum/ligand bonds still largely intact. Loss of individual aluminum-ligand units, as expected from unimolecular decomposition calculations, is not observed except following significant oxidation. These calculations highlight the role of the ligand in providing a steric barrier against oxidizers and in maintaining the large aluminum surface area of the solid-state cluster material. [http://dx

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Reactive sintering: An important component in the combustion of nanocomposite thermites

Cited by 144 publications

References 51 publications

A slice of an aluminum particle: Examining grains, strain and reactivity

A slice of an aluminum particle: Examining grains, strain and reactivity

Improving aluminum particle reactivity by annealing and quenching treatments: Synchrotron X-ray diffraction analysis of strain

Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

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