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Title Multi-scale modeling of thermochemical behavior of nano-energetic materials
URL
Publication Date
Date Accessioned
Degree PhD
Discipline/Department Aerospace Engineering
Degree Level doctoral
University/Publisher Georgia Tech
Abstract Conventional energetic materials which are based on monomolecular compounds such as trinitrotoluene (TNT) have relatively low volumetric energy density. The energy density can be significantly enhanced by the addition of metal particulates. Among all metals, aluminum is popular because of its high oxidation enthalpy, low cost, and relative safety. Micron-sized aluminum particles, which have relatively high ignition temperatures and burning times, have been most commonly employed. Ignition of micron-sized aluminum particles is typically achieved only upon melting of the oxide shell at 2350 K, thereby resulting in fairly high ignition delay. Novel approaches to reduce the ignition temperatures and burning times and enhance the energy content of the particle are necessary. Recently, there has been an enormous interest in nano-materials due to their unique physicochemical properties such as lower melting and ignition temperatures and shorter burning times. Favorably, tremendous developments in the synthesis technology of nano-materials have also been made in the recent past. Several metal-based energetic materials with nano-sized particles such as nano-thermites, nano-fluids, and metalized solid propellants are being actively studied. The “green” reactive mixture of nano-aluminum particles and water/ice mixture (ALICE) is being explored for various applications such as space and underwater propulsion, hydrogen generation, and fuel-cell technology. Strand burning experiments indicate that the burning rates of nano-aluminum and water mixtures surpass those of common energetic materials such as ammonium dinitramide (ADN), hydrazinium nitroformate (HNF), and cyclotetramethylene tetranitramine (HMX). Sufficient understanding of key physicochemical phenomena is, however, not present. Furthermore, the most critical parameters that dictate the burning rate have not been identified. A multi-zone theoretical framework is established to predict the burning properties and flame structure by solving conservation equations in each zone and enforcing the mass and energy continuities at the interfacial boundaries. An analytical expression for the burning rate is derived and physicochemical parameters that dictate the flame behavior are identified. An attempt is made to elucidate the rate-controlling combustion mechanism. The effect of bi-modal particle size distribution on the burning rate and flame structure are investigated. The results are compared with the experimental data and favorable agreement is achieved. The ignition and combustion characteristics of micron-sized aluminum particles can also be enhanced by replacing the inert alumina layer with favorable metallic coatings such as nickel. Experiments indicate that nickel-coated aluminum particles ignite at temperatures significantly lower than the melting point of the oxide film, 2350 K due to the presence of inter-metallic reactions. Nickel coating is also attractive for nano-sized aluminum particles due to its ability to maximize the active aluminum content. Understanding…
Subjects/Keywords Aluminum; Nano-particle; Molecular dynamics; Energetic materials; Nanostructured materials; Nanocomposites (Materials); Thermodynamics; Propellants; Combustion
Contributors Yang, Vigor (advisor); Seitzman, Jerry (committee member); Lieuwen, Timothy (committee member); Jagoda, Jechiel (committee member); Yetter, Richard (committee member)
Language en
Country of Publication us
Record ID handle:1853/50225
Repository gatech
Date Indexed 2018-01-11
Issued Date 2013-08-01 00:00:00
Note [degree] Ph.D.;

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…importance to both propulsion and material synthesis applications. The current understanding is, however, far from complete. In the present study, molecular dynamics simulations are performed to investigate the melting behavior, diffusion characteristics, and…

…temperature; (b) amorphous oxide layer with temperature and size dependent material properties. 159 Figure 7.9: Critical particle size predicted using the free-molecular heat transfer correlation in conjunction with temperature dependent…

…with a diameter of 100 nm and oxide layer thickness of 2.5 nm; (a) continuum-regime model, (b) free-molecular regime model. 172 Figure 8.4: Variation of temperature and oxide layer thickness with time for a particle with a diameter…

…of 5 m and oxide layer thickness of 2.5 nm; free-molecular regime model. 173 Figure 8.5: Effect of particle size on ignition temperature of aluminum particles in oxygenated environments. 174 xvi LIST OF SYMBOLS AND ABBREVIATIONS a lattice…

…chemical rate constant ka absorption coefficient ks scattering coefficient xvii kt extinction coefficient Kn Knudsen number L Lagrangian l1 vapor zone thickness l2 liquid zone thickness Lfus latent heat of fusion M molecular weight, mass…

…fictitious mass m mass, refraction index MW molecular weight N number of atoms NA Avogadro’s number Np particle number density Nstep number of time integration steps p momentum, pressure, vapor pressure Q energy, heat Qa absorption…

…lw liquid water m melting, mixture mol molecular ox oxidation, oxidizer, oxide p particle prod products r radiation, reaction reac reactants s shell xx u unburned v vapor, vaporization V water vapor zone vap vaporization w…

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