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Molecular Dynamics Simulations of th...

Witbeck, Brandon Wesley.

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Molecular Dynamics Simulations of the Impact of Defects on Ni/Al Nanolaminate Combustion.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Molecular Dynamics Simulations of the Impact of Defects on Ni/Al Nanolaminate Combustion./
Author:	Witbeck, Brandon Wesley.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
Description:	153 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-06, Section: B.
Contained By:	Dissertations Abstracts International82-06B.
Subject:	Nanoscience. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27831334
ISBN:	9798698595090

Molecular Dynamics Simulations of the Impact of Defects on Ni/Al Nanolaminate Combustion.
Witbeck, Brandon Wesley.

Molecular Dynamics Simulations of the Impact of Defects on Ni/Al Nanolaminate Combustion. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 153 p.

Source: Dissertations Abstracts International, Volume: 82-06, Section: B.

Thesis (Ph.D.)--University of Florida, 2020.

This item must not be sold to any third party vendors.

Ni/Al nanolaminates are reactive materials which have combustion characteristics that can be customized through changes to material microstructure. Models of these materials typically assume no crystal defects, which are known to form during fabrication. As such, the objective of this dissertation is to quantify the impact of these crystal defects on Ni/Al nanolaminate combustion. First, the role of point vacancies in Ni/Al nanolaminate combustion is investigated. Separate models of Ni/Al nanolaminates are populated with different excess vacancy concentrations and simulated in combustion reactions with different initial temperatures and hydrostatic pressures. Results show that increasing vacancy concentration increases reaction rates and peak temperatures, while bilayer thickness and thermodynamic boundary conditions are coupled to vacancy concentration effects on reaction rates. Secondly, the role of grain size in Ni/Al nanolaminate combustion is investigated. Nanolaminate models which contain polycrystalline Ni and Al layers are constructed with two different bilayer thicknesses, and each model is given a different uniform grain size. Combustion simulations reveal that Ni atoms diffuse preferentially along grain boundaries (GBs), which melt prior to Al grains and surround the grains in liquid Ni+Al solution. Decreasing grain size increases GB site density and increases reaction rates on the same order of magnitude as reductions in bilayer thickness, the primary nanolaminate structural feature. Finally, the role of GB structure in Ni/Al nanolaminate combustion is investigated in models containing bicrystal layers. Minimum GB energy structures are identified in Ni and Al models containing GBs with select misorientation angles. These structures are formed in models of Ni and Al layers, and layers with matching misorientations are joined into nanolaminate models and simulated in combustion reactions. Coefficients of Ni diffusion into Al are measured throughout combustion, and Arrhenius expressions are fit to coefficients during multiple periods of the reaction. Individual Arrhenius expressions are used to identify separate stages of combustion. Stage (i) and (ii) Arrhenius parameters reveal that increasing GB energy lowers activation energies and generally increases diffusion coefficients, while stage (iii) parameters show minimal influence from GB structure. Continuum models utilize these Arrhenius parameters to predict that GB structure impacts Ni/Al nanolaminate ignition temperatures without affecting combustion wave velocities.

ISBN: 9798698595090Subjects--Topical Terms:

587832
Nanoscience.
Subjects--Index Terms:

Combustion

Molecular Dynamics Simulations of the Impact of Defects on Ni/Al Nanolaminate Combustion.
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245 1 0 $a Molecular Dynamics Simulations of the Impact of Defects on Ni/Al Nanolaminate Combustion.
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300 $a 153 p.
500 $a Source: Dissertations Abstracts International, Volume: 82-06, Section: B.
500 $a Advisor: Spearot, Douglas E.
502 $a Thesis (Ph.D.)--University of Florida, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a Ni/Al nanolaminates are reactive materials which have combustion characteristics that can be customized through changes to material microstructure. Models of these materials typically assume no crystal defects, which are known to form during fabrication. As such, the objective of this dissertation is to quantify the impact of these crystal defects on Ni/Al nanolaminate combustion. First, the role of point vacancies in Ni/Al nanolaminate combustion is investigated. Separate models of Ni/Al nanolaminates are populated with different excess vacancy concentrations and simulated in combustion reactions with different initial temperatures and hydrostatic pressures. Results show that increasing vacancy concentration increases reaction rates and peak temperatures, while bilayer thickness and thermodynamic boundary conditions are coupled to vacancy concentration effects on reaction rates. Secondly, the role of grain size in Ni/Al nanolaminate combustion is investigated. Nanolaminate models which contain polycrystalline Ni and Al layers are constructed with two different bilayer thicknesses, and each model is given a different uniform grain size. Combustion simulations reveal that Ni atoms diffuse preferentially along grain boundaries (GBs), which melt prior to Al grains and surround the grains in liquid Ni+Al solution. Decreasing grain size increases GB site density and increases reaction rates on the same order of magnitude as reductions in bilayer thickness, the primary nanolaminate structural feature. Finally, the role of GB structure in Ni/Al nanolaminate combustion is investigated in models containing bicrystal layers. Minimum GB energy structures are identified in Ni and Al models containing GBs with select misorientation angles. These structures are formed in models of Ni and Al layers, and layers with matching misorientations are joined into nanolaminate models and simulated in combustion reactions. Coefficients of Ni diffusion into Al are measured throughout combustion, and Arrhenius expressions are fit to coefficients during multiple periods of the reaction. Individual Arrhenius expressions are used to identify separate stages of combustion. Stage (i) and (ii) Arrhenius parameters reveal that increasing GB energy lowers activation energies and generally increases diffusion coefficients, while stage (iii) parameters show minimal influence from GB structure. Continuum models utilize these Arrhenius parameters to predict that GB structure impacts Ni/Al nanolaminate ignition temperatures without affecting combustion wave velocities.
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653 $a Defects
653 $a Grains
653 $a Ignition
653 $a Nanolaminate
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690 $a 0215
710 2 $a University of Florida. $b Mechanical Engineering. $3 3350759
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