Kinetics of the reaction aluminum(2P0) + water over an extended temperature range

McClean, Roy E.; Nelson, H. H.; Campbell, Mark L.

doi:10.1021/j100140a024

Cited by 61 publications

(50 citation statements)

References 4 publications

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“…Reaction rates for reactions 17, 18, 19, and 20 were derived by Garland & Nelson (1992), Catoire et al (2003), andMcClean et al (1993). Destruction process for gas-phase AlO molecules are thermal fragmentation by the ambient gas, collisions with Compton electron, and reaction with He + .…”

Section: Aluminamentioning

confidence: 99%

The Chemistry of Population Iii Supernova Ejecta. Ii. The Nucleation of Molecular Clusters as a Diagnostic for Dust in the Early Universe

Cherchneff

Dwek

2010

ApJ

147

128

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We study the formation of molecular precursors to dust in the ejecta of Population III supernovae using a chemical kinetic approach to follow the evolution of small dust cluster abundances from day 100 to day 1000 after explosion. Our work focuses on zero-metallicity 20 M ⊙ and 170 M ⊙ progenitors, and we consider fully-macroscopically mixed and unmixed ejecta. The dust precursors comprise molecular chains, rings and small clusters of chemical composition relevant to the initial elemental composition of the ejecta under study. The nucleation stage for small silica, metal oxides and sulphides, pure metal, and carbon clusters is described with a new chemical reaction network highly relevant to the kinetic description of dust formation in hot circumstellar environments. We consider the effect of the pressure dependence of critical nucleation rates, and test the impact of microscopically-mixed He + on carbon dust formation. Two cases of metal depletion on silica clusters (full and no depletion) are considered to derive upper limits to the amounts of dust produced in SN ejecta at 1000 days, while the chemical composition of clusters gives a prescription for the type of dust formed in Pop. III supernovae.We show that the cluster mass produced in the fully-mixed ejecta of a 170M ⊙ progenitor is ∼ 25 M ⊙ whereas its 20 M ⊙ counterpart forms ∼ 0.16 M ⊙ of clusters. The unmixed ejecta of a 170 M ⊙ progenitor supernova synthesizes ∼ 5.6 M ⊙ of small clusters, while its 20 M ⊙ counterpart produces ∼ 0.103 M ⊙ . Our results point to smaller amounts of dust formed in the ejecta of Pop. III supernovae by a factor ∼ 5 compared to values derived by previous studies, and to different dust chemical composition. Such deviations result from some erroneous assumptions made, the inappropriate use of classical nucleation theory to model dust formation, and the omission of the synthethis of molecules in supernova ejecta. We also find that the unmixed ejecta of massive Pop. III supernovae chiefly form silica and/or silicates, and pure silicon grains whereas their lower mass counterparts form a dust mixture dominated by silica and/or silicates, pure silicon and iron sulphides. Amorphous carbon can only condense in ejecta where the carbon-rich zone is deprived of He + via the nucleation of carbon chains and rings characteristic of the synthesis of fullerenes. The first dust enrichment to the primordial gas in the early universe from Pop. III massive supernova comprises primarily pure silicon, silica and silicates. If carbon dust is present at redshift z > 6, alternative dust sources must be considered.

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Section: Aluminamentioning

confidence: 99%

The Chemistry of Population Iii Supernova Ejecta. Ii. The Nucleation of Molecular Clusters as a Diagnostic for Dust in the Early Universe

Cherchneff

Dwek

2010

ApJ

147

128

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“…Al atoms have been found to react with individual water molecules [1][2][3][4][5][6][7][8][9][10] and also in conditions of microhydration. [11][12][13] Relay (Grotthuss-type) mechanisms and tunneling play a role in those reactions, which are of technological and astrophysical importance; Al oxide and hydroxide have recently been detected in the space.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen migration dynamics in hydrated Al clusters: The Al17(−)·H2O system as an example

Álvarez‐Barcia¹,

Flores²

2014

The Journal of Chemical Physics

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The Alm((-))·(H2O)n systems are known to undergo water splitting processes in the gas phase giving HkAlm(OH)k((-))·(H2O)n-k systems, which can generate H2. The migration of H atoms from one Al atom to another on the cluster's surface is of critical importance to the mechanism of the complete H2 production process. We have applied a combination of Molecular Dynamics and Rice-Ramsperger-Kassel-Marcus theory including tunneling effects to study the gas-phase evolution of HAl17(OH)((-)), which can be considered a model system. First, we have performed an extensive search for local minima and the connecting saddle points using a density functional theory method. It is found that in the water-splitting process Al17((-))·(H2O) → HAl17(OH)((-)), the H atom which bonds to the Al cluster losses rather quickly its excess energy, which is easily "absorbed" by the cluster because of its flexibility. This fact ultimately determines that long-range hydrogen migration is not a very fast process and that, probably, tunneling only plays a secondary role in the migration dynamics, at least for moderate energies. Reduction of the total energy results in the process being very much slowed down. The consequences on the possible mechanisms of H2 generation from the interaction of Al clusters and water molecules are discussed.

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“…The HAlOH* intermediate was observed by McClean et al. after reaction of aluminum atoms with H 2 O formed from the photolysis of triethylaluminium 9. The dissociation of HAlOH to H + AlOH is predicted by Sharipov to be fast, and the recombination reaction to AlO + H 2 is slow, so this is possibly the overall rate‐determining step (RDS) 10.…”

Section: Methodsmentioning

confidence: 94%

“…This result suggests that R5 is relatively slow compared to either R2 or R3, and AlO can reform at combustion temperatures because of dissociation of Al 2 O 3 6. Detailed steps of R2 are described experimentally by McClean et al.,9 and theoretically by Sharipov et al 10…”

Section: Methodsmentioning

confidence: 97%

Evidence of a Kinetic Isotope Effect in Nanoaluminum and Water Combustion

2014

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The normally innocuous combination of aluminum and water becomes violently reactive on the nanoscale. Research in the field of the combustion of nanoparticulate aluminum has important implications in the design of molecular aluminum clusters, hydrogen storage systems, as well as energetic formulations which could use extraterrestrial water for space propulsion. However, the mechanism that controls the reaction speed is poorly understood. While current models for micron‐sized aluminum water combustion reactions place heavy emphasis on diffusional limitations, as reaction scales become commensurate with diffusion lengths (approaching the nanoscale) reaction rates have long been suspected to depend on chemical kinetics, but have never been definitely measured. The combustion analysis of nanoparticulate aluminum with H2O or D2O is presented. Different reaction rates resulting from the kinetic isotope effect are observed. The current study presents the first‐ever observed kinetic isotope effect in a metal combustion reaction and verifies that chemical reaction kinetics play a major role in determining the global burning rate.

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Kinetics of the reaction aluminum(2P0) + water over an extended temperature range

Cited by 61 publications

References 4 publications

The Chemistry of Population Iii Supernova Ejecta. Ii. The Nucleation of Molecular Clusters as a Diagnostic for Dust in the Early Universe

The Chemistry of Population Iii Supernova Ejecta. Ii. The Nucleation of Molecular Clusters as a Diagnostic for Dust in the Early Universe

Hydrogen migration dynamics in hydrated Al clusters: The Al17(−)·H2O system as an example

Evidence of a Kinetic Isotope Effect in Nanoaluminum and Water Combustion

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