Degree Type

Dissertation

Date of Award

2013

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Valery Levitas

Abstract

Aluminum nanoparticles are of interest due to the variety of their applications, including additives for plastics and powder metallurgy. They can also enhance the burning rate of propellants. Metallic particles in traditional thermites are in the micron size range. When the particle diameter reduces to the nanometer range, their reactivity increases by several orders of magnitude. Thus flame rates of 0.9-1 km/s can be reached, while for micron size thermites they are on the order of centimeters or meters per second. Ignition delay time also decreases by up to three orders of magnitude.

The two main continuum methods to study melting-related phenomena (like surface melting, size dependence of melting temperature, melting of a few nm-size particles, and overheating at a very fast heating rate) are the sharp interface method and the phasefield approach. The sharp interface approach fails when nanoparticles and solid-liquid interface radii are comparable with interface width and also when nanoparticles are overheated fast. In the phase field model, the interface between phases has a finite thickness in which physical quantities, such as elastic moduli and entropy, vary between their values in the adjacent bulk phases. An order parameter describe the material instabilities, such as the instabilities of a crystal lattice in solid-solid phase transformations, melting, fracture and so on. Phase field method provides smooth description of the phase interface, rather than discontinuous one. We developed an advanced phase field model coupled to mechanics to study melting in the region of metastability and complete instability of solid and melt.

Copyright Owner

Kamran Samani

Language

en

Date Available

June 1, 2014

File Format

application/pdf

File Size

84 pages

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