Highly reactive energetic films by pre-stressing nano-aluminum particles

Bello, Michael N.; Williams, A. M.; Levitas, Valery I.; Tamura, Nobumichi; Unruh, Daniel K.; Warzywoda, Juliusz; Pantoya, Michelle L.

doi:10.1039/c9ra04871e

Cited by 7 publications

(12 citation statements)

References 28 publications

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“…Particle size distributions are shown in Supplementary Information , Figure S1 with the measured mean diameter and standard deviation reported in Table 1 along with the label identifier for each powder. The annealing and quenching process does not alter the size distribution and this was confirmed previously for nAl powders in Bello et al [12] and μAl powders in McCollum et al [13].…”

Section: Methodssupporting

confidence: 78%

“…The shell becomes delaminated from the core and is theorized to fracture more easily. The core-shell delamination in SQÀ Al is a function of Al particle size because μAl has shown 52 % core-shell interfacial surface area delamination [9] while nAl has shown 81 % core-shell interfacial surface area delamination [12]. Without support from the core, the shell more easily fractures thereby enhancing diffusion controlled reactions.…”

Section: Introductionmentioning

confidence: 99%

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On the Pressure Generated by Thermite Reactions Using Stress‐Altered Aluminum Particles

Williams

Shancita

Altman

et al. 2020

Propellants Explo Pyrotec

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This study examines pressure build-up and decay in thermites upon impact ignition and interprets reactivity based on the holistic pressure history. The thermite is a mixture of aluminum (Al) combined with bismuth trioxide (Bi 2 O 3) powder. Four different Al particles sizes were examined that ranged from 100 nm to 18.5 μm mean diameter and for each size, two different Al powder treatments were examined: stress-altered compared to untreated, as-received Al powder. Stress-altered Al powders have been shown to be more reactive, such that the stress-altered Al powder thermites offer a metric for analyzing thermite reactivity in terms of pressure development compared to untreated Al powder. In a binary thermite system, multiple phase changes and interface chemistry influence the transient pressure response during reaction. Results reveal three key pressure metrics that need consideration specifically for thermite combustion: (1) delay time to peak pressure, (2) peak pressure, and (3) decay after peak pressure. Our experiments show that a lower peak pressure corresponds with higher thermite reactivity because aluminum consumption of oxygen generated by decomposing solid oxidizer reduces the peak pressure. Faster rates of reaction consume oxygen at higher rates such that pressure development becomes more limited than less reactive thermites and the result is a lower peak pressure. This conclusion is opposite of traditional studies using metal fuels with a gaseous environment that typically show higher peak pressures correspond with greater reactivity.

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Section: Methodssupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

On the Pressure Generated by Thermite Reactions Using Stress‐Altered Aluminum Particles

Williams

Shancita

Altman

et al. 2020

Propellants Explo Pyrotec

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“…The thermal processing of Al powder, specifically its annealing followed by fast quenching had been developed by Hill et al [19]. A number of subsequent studies further demonstrated distinctly different performance of as-received (i. e., called UN, untreated) and thermally processed (i. e., called SQ, super-quenched) powders in different energetic formulations [20,21,23]. Thermal processing the powder resulted in high internal particle stress [19,23], but a link to the mechanism for performance variation remained unclear.…”

Section: Effect Of Thermal Processing Of Al Powder On the Materials R...mentioning

confidence: 99%

“…A number of subsequent studies further demonstrated distinctly different performance of as-received (i. e., called UN, untreated) and thermally processed (i. e., called SQ, super-quenched) powders in different energetic formulations [20,21,23]. Thermal processing the powder resulted in high internal particle stress [19,23], but a link to the mechanism for performance variation remained unclear. Recently, we demonstrated that thermal processing also affected surface energy which was linked to low-temperature reactivity of the powder [24,25].…”

Section: Effect Of Thermal Processing Of Al Powder On the Materials R...mentioning

confidence: 99%

Comprehending Metal Particle Combustion: a Path Forward

Altman

Pantoya

2022

Propellants Explo Pyrotec

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The paper discusses the physics required for accurate modeling of metal particle combustion and includes aspects previously neglected. Specifically, three physical phenomena are emphasized: 1) internal boiling on the condensed oxide-metal interface; 2) condense-luminescent loss during nano-oxide formation; and, 3) suppressed heat transfer on the metal particle surface due to a low energy accommodation coefficient (EAC) are essential. The last two phenomena were explored in previous work. Internal particle interface boiling detailed in the current work enables the semi-heterogeneous combustion of Al particles, an im-portant process needing attention for accurate modeling. The interface boiling mechanism allowing for the semi-heterogeneous combustion explains a number of experimental puzzles related to metal particle combustion. In particular, the semi-heterogeneous combustion justifies the coexistence of two burning regimes of Al particles (slow and fast) recently observed. Based on reported findings, revising current numerical models for metal particle combustion to include these three physical phenomena is necessary. Implications toward enhancement of energetic performance for metal-containing formulations are also discussed.

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“…Several studies have focused on improving the reactivity of Al nanoparticles by their microstructural alteration through induction of thermomechanical stresses. − The core of the Al nanoparticles nominally exists under tensile stress at room temperature, which attains a zero-strain state when heated to ∼673 K . It has been observed that preannealing of Al nanoparticles at around ∼673 K for several minutes followed by fast quenching induces dilatational lattice strain on the core, which appears to enhance Al transport through the shell. − Additionally, an investigation on aging behavior of nanothermite composites of Al with oxidizers such as CuO, Fe 2 O 3 , and Co 3 O 4 , by annealing of the mixtures at ∼473 K for 15 days, showed that the alumina shell became nonuniform in thickness . The nonuniformity in the thickness of the shell led to a higher mass transport rate of Al through the thinner regions, resulting in an unexpectedly high reactivity of the annealed nanothermite composites.…”

Section: Introductionmentioning

confidence: 99%

In-Situ Thermochemical Shock-Induced Stress at the Metal/Oxide Interface Enhances Reactivity of Aluminum Nanoparticles

Biswas

Ghildiyal

et al. 2022

ACS Appl. Mater. Interfaces

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Although aluminum (Al) nanoparticles have been widely explored as fuels in energetic applications, researchers are still exploring approaches for tuning their energy release profile via microstructural alteration. In this study, we show that a nanocomposite (∼70 nm) of a metal ammine complex, such as tetraamine copper nitrate (Cu(NH 3 ) 4 (NO 3 ) 2 /TACN), coated Al nanoparticles containing only 10 wt. % TACN, demonstrates a ∼200 K lower reaction initiation temperature coupled with an order of magnitude enhancement in the reaction rate. Through time/temperature-resolved mass spectrometry and ignition onset measurements at high heating rates, we show that the ignition occurs due to a condensed phase reaction between Al and copper oxide (CuO) crystallized on TACN decomposition. TEM and XRD analyses on the nanoparticles at an intermediate stage show that the rapid heat release from TACN decomposition in-situ enhances the strain on the Al core with induction of nonuniformities in the thickness of its AlO x shell. The thinner region of the nonuniform shell enables rapid mass transfer of Al ions to the crystallized CuO, enabling their condensed phase ignition. Hence, the thermochemical shock from TACN coating induces stresses at the Al/AlO x interface, which effectively switches the usual gas phase O 2 diffusion-limited ignition process of Al nanoparticles to become condensed phase Al ion transfer controlled, thereby enhancing their reactivity.

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Highly reactive energetic films by pre-stressing nano-aluminum particles

Abstract: Energetic films were synthesized using stress altered nano-aluminum particles (nAl).

Cited by 7 publications

References 28 publications

On the Pressure Generated by Thermite Reactions Using Stress‐Altered Aluminum Particles

On the Pressure Generated by Thermite Reactions Using Stress‐Altered Aluminum Particles

Comprehending Metal Particle Combustion: a Path Forward

In-Situ Thermochemical Shock-Induced Stress at the Metal/Oxide Interface Enhances Reactivity of Aluminum Nanoparticles

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