Oxygen Hopping Mechanism for Thermal Expansion Coefficient of Mullite Using Atomistic Simulation
Date Issued
2009
Date
2009
Author(s)
Wu, Chien-Cheng
Abstract
Mullite is the major phase of many conventional silicate-based ceramics (e.g., porcelains and aluminosilicate refractory) and of various advanced ceramics, coatings, fibers and ceramic matrix composites. The high creep resistance and thermal/chemical stability of mullite have made it one of the best candidates for structural and high-temperature applications. Recently, a few anomalies associated with mechanical and thermal properties of mullite have been identified. In this thesis, the anomaly related to thermal expansion was studied using molecular dynamics simulation. The oxygen vacancy hopping mechanisms and their correlation with the anomaly were investigated. The Matsui interatomic potential was adapted herein. We calculated lattice constants of sillimanite and mullite at difference temperatures. The calculated results agreed well with the experiment measurements. Thermal expansion anomaly at high temperature was found in mullite but not in sillimanite. Oxygen vacancy densities were plotted. The dynamic site-exchange processes between O(C) and vacancy sites were found in mullite. These microscopic processes resulted in thermal expansion anomaly.
Subjects
Mullite
vacancy
hopping
molecular dynamics
lattice constants
coefficient of thermal expansion
Type
thesis
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