Award Date

2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical Engineering

Advisor 1

Yitung Chen, Committee Chair

First Committee Member

Robert Boehm

Second Committee Member

William Culbreth

Third Committee Member

Anthony Hechanova

Graduate Faculty Representative

John W. Farley,

Number of Pages

167

Abstract

Oxidation modeling is normally engineered to study systems at macroscopic scales, mostly in analytical forms based on diffusion theories. The associated time scale is usually in months, days, or minutes, and the length scale is in the order of microns. In this dissertation, oxidation modeling is performed at atomistic scale with the time and length scales in picoseconds and angstroms, respectively, using molecular dynamics. Molecular dynamics simulations generate trajectories of each atom or particle in a system according to the laws of physics. Studying oxidations under the atomistic point of view can offer new insights on atomic behaviors and influencing factors in oxidation mechanisms.

This dissertation focuses on modeling dynamic behaviors of liquid lead, oxygen, and iron. Lead is used as a coolant in nuclear reactors due to its excellent physical properties such as high boiling point and neutron transparency. Nevertheless, liquid lead is very corrosive to iron, the main structural material in reactors. As lead diffuses along grain boundaries and other faults in iron crystals, iron lattices become brittle. In addition, oxygen dissolving in liquid lead causes another problem. Too much oxygen promotes undesired compound formations of lead oxide, typically known as slags, which hinder the coolant flow. However, when only traces of oxygen are present in this lead-iron system, protective iron oxide layers form and help preventing further ingress of liquid lead.

This dissertation provides a new approach in modeling oxidations, using the Generalized Reduced Gradient (GRG) method in minimizing the potential energy of a metal/metal oxide system. The approach is then applied to model iron oxidation in the form of magnetite. Finally, a system consisting of liquid lead, iron, and oxygen is studied under several scenarios.

Keywords

Atomic behaviors; Constrained optimization; Corrosion; Generalized reduced gradient; Iron; Lead slags; Liquid lead coolants; Magnetite; Molecular dynamics; Oxidation; Protective oxide layer

Disciplines

Materials Science and Engineering | Mechanical Engineering | Nuclear Engineering

Language

English


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